In T 598/99 the board observed that the principle of reformatio in peius applied so as to prevent a sole appellant being put in a worse situation than he was in before he appealed. Where the patentee was the sole appellant, the principle could not serve to protect the opponent (respondent) from being put in a worse situation than he was in before the appeal (G 9/92 date: 1994-07-14, OJ 1994, 875 and G 4/93, OJ 1994, 875). Indeed, whenever a sole patentee was successful in his appeal against the revocation of his patent, the opponent would be in a worse position than before. The fact that the opponent was not entitled to appeal against the decision to revoke the patent was immaterial in that respect.

An early decision applying the principles expounded in G 9/92 date: 1994-07-14 and G 4/93 (OJ 1994, 875) was T 856/92, in which the board concluded that in a case where the patentee and sole appellant appealed only in respect of some of the claims held allowable in the opposition division's interlocutory decision, neither the board nor the opponent might challenge those claims not questioned by the appellant.

When the patent proprietor is the sole appellant, the patent as maintained by the opposition division in its interlocutory decision cannot be objected to by the board, either at the request of the respondent (opponent) or ex officio (see G 1/99, OJ 2001, 381, T 1689/12).

In T 1626/11, the first ten claims of the main request were identical in wording to those of the second auxiliary request, which the opposition division had already found to comply with the EPC. Faced with the question whether it could examine those claims without contravening the principle of no reformatio in peius, the board cited T 856/92 and T 149/02, in which the boards had concluded that, where the proprietor was the sole appellant, they could no longer review any part of a set of claims included in a new set of claims also containing additional (parallel) claims if the opposition division had already held that the first set to be EPC-compliant and the additional claims did not alter how it was to be interpreted. This conclusion, based on G 9/92 date: 1994-07-14, was similarly reached in T 168/04, T 1713/08, T 722/10 and T 428/12.

The board in T 659/07 found that where the patentee is the sole appellant, the patent as maintained by the opposition division in its interlocutory decisions, cannot be objected to by the board, either at the request of the respondent (opponent) or ex officio, even if the patent as maintained would otherwise have to be revoked on the ground that a feature present in both claim 1 as granted and as maintained introduces added subject-matter contrary to Art. 123(2) EPC 1973.