The Enlarged Board in G 1/93 (OJ 1994, 541) mentioned three instances where the patent could be maintained:

- If the added feature could be replaced by another feature disclosed in the application as filed without breaching Art. 123(3) EPC 1973, the patent could be maintained (in amended form). This might turn out to be a rare case in practice (see below T 166/90).

- An added undisclosed feature without any technical meaning could be deleted from a claim without violating Art. 123(3) EPC 1973.

- An added feature, which did not provide a technical contribution to the subject-matter of the claimed invention but merely limited the protection conferred by the patent as granted by excluding protection for part of the subject-matter of the claimed invention as covered by the application as filed, was not considered as subject-matter which extended beyond the content of the application as filed within the meaning of Art. 123(2) EPC 1973. In this case also the patent could be maintained. See below, chapter II.E.3.3. "Addition to the claim of an undisclosed feature limiting protection conferred, without providing a technical contribution".

The board noted in T 335/03 that, according to G 1/93, there was no basis in the Convention for providing a claim with a footnote to the following effect; "This feature is the subject of an inadmissible extension. No rights may be derived from this feature"; in other words, in cases of conflict between Art. 123(2) and Art. 123(3) EPC 1973 the footnote solution is inadmissible (see also T 307/05 and T 614/12).

In T 10/91 a neutral feature of no particular value for the skilled person was added during the examination proceedings. The feature had no technical significance. It could therefore stay in the claim, but could not be taken as delimiting when examining for novelty and inventive step.

In T 938/90, however, the addition was technically significant and it had to be taken into account in the examination for novelty and inventive step. The board therefore declined to apply the principles developed in T 231/89 and dismissed the patent proprietor's appeal against the revocation of the patent (see T 493/93).

In T 166/90 the board allowed an inadmissible feature in a granted claim to be replaced by other disclosed features, since this did not extend the scope of protection. The invention concerned an opaque plastic film. The product claim as granted contained a feature stating that the density of the film was less than the arithmetical density from the type and proportion of the individual components. In opposition proceedings the patent proprietor claimed a process for manufacturing the film, but without including in his process claim the density-related feature. The board examined whether this would broaden the scope of the patent, asking if the process claim features which replaced the deleted feature necessarily limited the claim to films – like that in the granted product claim – with a density less than the arithmetical one. The board concluded that, with a probability bordering on certainty, the process now claimed would produce an opaque film of a density less than that arithmetically derivable from the type and proportion of its individual components. Thus, deleting the density-related feature had not in fact extended the scope of protection.

Decision T 438/98 followed T 271/84 (OJ 1987, 405), T 371/88 (OJ 1992, 157), T 673/89 and T 214/91, in ruling that amending a claim to remove an inconsistency did not contravene Art. 123(2) or Art. 123(3) EPC 1973 if the claim as corrected had the same meaning as the correct interpretation of the uncorrected claim in the light of the description. For another case concerning the conflict between Art. 123(2) and (3) EPC, see T 1202/07, which refers to T 1018/02 (extent of protection conferred by a claim feature not consistent with the description). The latter decision dealt in detail with interpretation of claims and can thus be distinguished from, in particular, T 438/98 (correction of an obvious clerical error).

In T 553/99 the board stated that if a claim as granted contained an undisclosed, limiting feature in contravention of Art. 123(2) EPC 1973 it could be maintained in the claim without violating Art. 123(2) EPC 1973 provided that a further limiting feature was added to the claim which further feature was properly disclosed in the application as filed, and deprived the undisclosed feature of all technical contribution to the subject-matter of the claimed invention.

T 942/01 held it to be a principle in patent law (see for example G 1/93, OJ 1994, 541) that a patent could not be maintained unamended in opposition procedure if a violation of Art. 123(2) EPC 1973 had occurred during the examination procedure. A cancellation of unallowable amendments during the opposition proceedings was normally possible under the provisions of the Convention, except where the unallowable amendment was a "limiting extension", so that its cancellation would extend the protection conferred by the patent and therefore contravene the requirements of Art. 123(3) EPC 1973 (G 1/93). However, the case at issue dealt with an unallowable extension only. The feature, which was present in the claim of the application as filed and now reintroduced in the claim, did not extend the protection conferred by the claims but rather restricted it.

T 567/08 gives an example of a "limiting extension" adding subject-matter contrary to Art. 123(2) EPC but at the same time limiting the scope of protection vis-à-vis what could have been claimed, so that its removal infringed Art. 123(3) EPC.

In T 250/05 the board, following the principles set out in G 1/93, came to the conclusion that the patent could not be maintained unamended and that the patent could only be maintained if there was a basis in the application as filed for replacing such subject-matter without violating Art. 123(3) EPC. The sixth auxiliary request (which contained only one claim) met both prerequisites.

In T 195/09, on the conflict between Art. 123(2) and (3) EPC, the appellant referred to T 108/91 in which it had been decided that an inaccurate technical statement in a granted claim, which statement was evidently inconsistent with the totality of the disclosure of the patent and would contravene the requirements of Art. 123(2) EPC, could be replaced with an accurate statement of the technical features involved without infringing Art. 123(3) EPC. The board in T 195/09 pointed out that this decision had been clearly overruled by G 1/93 (on T 108/91, see also T 1202/07, T 1896/11).

In T 1180/05 the board, on the basis of decisions G 1/93 and G 1/03 dealing with Art. 123(2) and (3) EPC 1973 and with disclaimers, came to the conclusion that the deletion of a feature in a granted claim, which feature extended beyond the content of the application as filed, and its reintroduction in the form of a disclaimer, so that the subject-matter of the claim remained the same, was not suitable to overcome the potential conflict between Art. 123 paragraphs 2EPC 1973 and Art. 123 paragraphs 3 EOC 1973 of Art. 123 EPC 1973. The board decided not to refer the question to the Enlarged Board of Appeal as requested by the patent proprietor. The decision of the opposition division maintaining the patent in amended form was set aside and the patent revoked.