In T 552/91 (OJ 1995, 100) the question arose as to whether and in what form protection could be obtained for groups of chemical substances and individual compounds whose originally disclosed structural formula proved incorrect. The applicant's main request was aimed at securing such protection by a further substance claim for the group of compounds with the structural formula subsequently found to be correct. This request was refused on the grounds that it would violate Art. 123(2) EPC 1973. The board defined "content" within the meaning of Art. 123(2) EPC 1973 as "the entire technical disclosure derived by a skilled person from the application" (on the notion of "content", see also II.E.1.1.1). Thus it was not enough to prove that as a result of amendments to the original patent application nothing other than the originally disclosed subject-matter was claimed; what was more important was that technically relevant information which the skilled person could not derive from the original documents was not thereby added to the application. In this case, the subsequently amended general formula gave the skilled person for the first time crucial information about the true chemical structure of the group of substances. This led to conclusions regarding properties that could be put to use. The information added to the application through the amendment of the general formula and relating to the true composition of the group of substances could not have been obtained from the application as originally filed (for decisions referring to T 552/91, see T 1074/97 and T 2003/07).
T 1728/07 gives a more recent example of the correction of an error in a formula. The sole objection raised under Art. 100(c) EPC in this case concerned the question of whether or not the amendments to the structural formulae representing oxazoline derivatives, found to be allowable under R. 88 EPC 1973 (now R. 139 EPC) during examination proceedings, introduced subject-matter extending beyond the content of the application as filed. According to R. 139 EPC, second sentence, it must be immediately apparent to the skilled person that (i) an error has occurred and (ii) how it should be corrected. The board concluded that the skilled person would have no doubt that an error had occurred in the structure depicted for formula (I) as originally filed (cf. requirement (i)). With respect to requirement (ii), it must be decided whether the corrected feature is directly and unambiguously derivable from the content of the application as originally filed taken as a whole. This requirement was also found by the board to be fulfilled. Hence the amendment to formula (I) was allowable.