If no evidence of legal succession is produced, the mere declaration by a company designated as legal successor to the original opponent that it is the original opponent's legal successor is not sufficient to substantiate the transfer of the status of opponent and of party to the appeal proceedings (T 670/95).
In T 261/03 (of 24 November 2005) the board of appeal considered what kind of evidence was required to establish a valid transfer. The board made a parallel to the requirements of R. 20 EPC 1973 and noted that it was not aware of any appeal decision that had held that the documents to be submitted according to this provision have to prove the alleged transfer "up to the hilt". Such a yardstick of full and absolute proof would indeed be overly strict since in many situations documentary evidence alone could then hardly suffice. As the wording of R. 20(1) EPC 1973 suggested, something less was required. The board took the view that the requirements of R. 20 EPC 1973 were complied with if the documents submitted were such as to render it credible to the competent organ of the EPO, evaluating the documents in a reasonable way and in the light of all the circumstances, that the alleged facts are true. The mere fact that another document might have been a more direct piece of evidence than the one submitted by the appellant does not invalidate the proof actually offered (see T 273/02, applied in T 1178/04).