Limited exceptions to the rule against reformatio in peius exist. In G 1/99 (OJ 2001, 381) the Enlarged Board of Appeal answered the question referred to it in T 315/97 date: 1998-12-17 (OJ 1999, 554), namely, "Must an amended claim which would put the opponent and sole appellant in a worse situation than if he had not appealed – e.g. by deleting a limiting feature of the claim – be rejected?".

The Enlarged Board held that in principle such a claim must be rejected. However, an exception to this principle might be made where the opposition division had allowed an inadmissible amendment. In the case at issue the opposition division had done just that with the agreement of the proprietor, who was thus not adversely affected by the decision and unable to appeal. The patent proprietor (respondent) had filed during the appeal proceedings a main request including the added (and unallowable) limiting feature, and an auxiliary request deleting it (and thus widening the claim). The Enlarged Board found that the main request had to be rejected because it did not meet the requirements of the EPC. Moreover, if the principle of reformatio in peius were to be applied without considering the specific circumstances of the case, the auxiliary request would also have to be rejected because it would put the opponent (appellant) in a worse situation than if it had not appealed. The only possible course the board could then take would be to revoke the patent, there being no further remedy for the proprietor. The proprietor would thus definitively lose any protection as a direct consequence of an inadmissible amendment being held allowable by the opposition division. The Enlarged Board considered it inequitable for the patent proprietor not to be given a fair opportunity to mitigate the consequences of errors of judgment made by the opposition division. The patent proprietor should thus be allowed to file requests in order to overcome this deficiency, as follows:

- in the first place, for an amendment introducing one or more originally disclosed features which limited the scope of the patent as amended;

- if such a limitation was not possible, for an amendment introducing one or more originally disclosed features which extended the scope of the patent as maintained, but within the limits of Art. 123(3) EPC 1973;

- finally, if such amendments were not possible, for deletion of the inadmissible amendment, but within the limits of Art. 123(3) EPC 1973, even if, as a result, the situation of the opponent was made worse.

See T 594/97, T 994/97, T 590/98, T 76/99 and T 724/99 for application of the principles enunciated in G 1/99.

The three options given in G 1/99 were set out with regard to the requirement of Art. 123(2) EPC. According to T 648/15 these options could be applied in a similar way when dealing with the requirement of Art. 84 EPC (see also T 1380/04). The board further noted, that the three options given in G 1/99 do not apply independently of one another and cannot be chosen ad libitum. Indeed, they are set out in such a way so as to indicate a particular sequence of options for overcoming the deficiency presented by a claim.

According to T 809/99 a non-appealing patent proprietor is primarily restricted on appeal to defending the claims as maintained by the opposition division. If these claims are not allowable, the principle of prohibition of reformatio in peius applies, i.e. an amended claim which would put the opponent and sole appellant in a worse situation than if it had not appealed must be rejected. The board went on to say that the only exception to this principle as set out in G 1/99 requires consideration of a particular sequence of possibilities for overcoming the deficiency presented by the claim(s). The first solution for overcoming the deficiency to be considered (an amendment introducing one or more originally disclosed limiting features which would not put the opponent (appellant) in a worse situation than it was in before it appealed) in fact concerns a limitation of the scope of the claim. Such limitation can also be achieved by deleting the alternative embodiment in the claim, which led to the deficiency. The proprietor's argument that the limitation to only one of the two alternatives would render the scope of protection too narrow for it to be commercially interesting is not a valid reason for dismissing this solution and proceeding to the next possible solution indicated in G 1/99.

The board in T 1033/08 made it clear that G 1/99 (OJ 2001, 381) did not supersede G 9/92 date: 1994-07-14 and G 4/93 (both in OJ 1994, 875), but was complementary thereto in that it gave directions for allowing an exception to the principle of prohibition of reformatio in peius as defined in these decisions. Certain conditions had to be fulfilled. A limiting feature introduced during the opposition procedure had to be deleted. The necessity for its deletion had to be caused by the appeal. This meant that the deletion was necessary and appropriate because it was related to a ground of opposition and caused by new facts, evidence or arguments put forward by the appellant, or because of a different evaluation of the situation by the board of appeal. Without the deletion, the patent would have to be revoked. It was not possible to overcome the objection by introducing new features which limit the scope of the patent as maintained. Only if these preconditions were fulfilled, might an objection be overcome by introducing new features which extended the scope of the patent as maintained, but within the limits of Art. 123(3) EPC according to the second option of G 1/99.

In T 974/10 the board emphasised that the Enlarged Board of Appeal had stated in G 1/99 that, "... if the patent cannot be maintained for reasons which were not raised at the first instance, the non-appealing proprietor deserves protection for reasons of equity". As, in the case at issue, the clarity objection was raised by the board for the first time in the appeal, the respondent had to be allowed to file amendments as foreseen in decision G 1/99, which decision gave due regard to the principle of equity.

According to T 1843/09 (OJ 2013, 502) the prohibition of reformatio in peius as far as it entails a procedural limitation of the proprietor's liberty to change by way of amendments the scope of protection sought prevails "in principle" (G 4/93, OJ 1994, 875) until the final settlement of the opposition case and, therefore, also in any proceedings, including further appeal proceedings, subsequent to a remittal under Art. 111 EPC. The board went on to say that it is clear from G 1/99 that exceptions to the principle of the prohibition of reformatio in peius are a matter of equity in order to protect the non-appealing proprietor against procedural discrimination in circumstances where that prohibition would impair the legitimate defence of its patent. Therefore, exceptions are not limited to the situation specifically dealt with in G 1/99. Rather, the equity approach as taken by the Enlarged Board of Appeal covers, beyond an error of judgment by the opposition division, any change of the factual and/or legal basis on which limitations have been made by the proprietor prior to the appeal by the opponent as the sole appellant, provided the proprietor would be prevented by the prohibition on reformatio in peius from adequately defending its patent against new facts and objections introduced into the proceedings at the appeal stage.

In T 24/13, the appellant had asserted that a remittal under Art. 111 EPC would also put it at a disadvantage as the proprietor might possibly be granted a broader patent. The board disagreed because the prohibition on reformatio en peius applied equally in opposition proceedings resumed after such remittal (see T 1843/09, OJ 2013, 508; T 1033/08).

In T 61/10 the board pointed out that the existence of a causal link between the limiting feature to be deleted and the new situation arising on appeal was a necessary precondition for justifying an exception to the principle of prohibition of reformatio in peius for reasons of equity. In G 1/99, T 1843/09 and T 1979/11 this condition was fulfilled. However, in the case before the board, the precondition was not fulfilled, so a departure from the principle of prohibition of reformatio in peius based on analogies with the cases cited was not justified.

In T 2129/14 the inadmissible amendment concerned four elements of the claimed system and some relationships between them. Compared with claim 1 of the request found allowable by the opposition division, in claim 1 of the second auxiliary request three features were deleted. As a result, the protection was extended compared to the request on the basis of which the patent would have been maintained if the opponent and sole appellant had not appealed. Under such circumstances the opponent and sole appellant was in a worse situation than if it had not appealed. The Enlarged Board laid down the conditions under which the exception may be made. The board noted that the three conditions laid down by G 1/99 are sequential. Further, the board noted that in claim 1 of the second auxiliary request features had been added which also involved some relationships between the four elements of the system. In the board's opinion, each of the requirements lost by deleting the inadmissible amendment had to be considered together with the added features, in the light of the conditions established in G 1/99. The board came to the conclusion that the amendments fell within the conditions for an allowable exception under G 1/99, allowing the deletion of the former inadmissible amendments, and were therefore allowable.