The admissibility of the opposition must be checked ex officio in every phase of the opposition and ensuing appeal proceedings. It can and, where appropriate, must be raised by the board in appeal proceedings even if this is the first time this matter is addressed (T 289/91, OJ 1994, 649; T 28/93 and T 522/94, OJ 1998, 421).
The board in T 15/01 (OJ 2006, 153) held that the same principles applied a fortiori to the examination of the admissibility of an appeal. The appellant's procedural objection against the late introduction of the issue at a rather late stage of the appeal proceedings could not therefore succeed; admissibility issues can and have to be examined at every stage of the appeal procedure. The admissibility of an appeal had been called into question with the argument that the appeal was filed on behalf of a legal entity which had already ceased to exist due to a merger.
This was confirmed in T 1668/07, where the board therefore had to consider the respondent's new main request that the appeal be deemed inadmissible, although it was filed long after the periods for filing an appeal had expired and after oral proceedings had been arranged.