The question of what is a validly claimed convention priority came up in Preprogenia/Collaborative.[1] It was held that for priority to be established, "the subject matter of the claims of the European application must be clearly identifiable in the documents of the previous application as a whole. Identical wording is not required. However, if any essential element of the invention for which a European patent is sought is missing, there is no right to priority." The Board agreed that in some cases features might be implied, so long as the implication was "direct and unambiguous," but matter that was omitted, and only recognized as being essential later, could not be implied as being present.

In Hepatitis B/Biogen a claim to a recombinant DNA molecule capable of coding for a particular protein was found to be supported by a priority document notwithstanding the fact that the priority document lacked any data on production of the protein in question.[2] The English Court of Appeal reached an exactly contrary decision on the same patent in Biogen v. Madeva.[3] The EPO agreed, however, that a claim to a specific amino acid sequence is not supported by a priority document in which a sequence was given but differed in three amino acids out of a total of 527, even though following the teaching given the desired product could have been obtained. In the Board's view, the structure set out in the claim was part of its essential technical content and since this was not present in the priority document, priority could not validly be claimed from such document.[4]