Objections to the clarity of claims or any consequent requests for amendment are only relevant to opposition proceedings in so far as they can influence the decisions on issues under Art. 100 EPC or arise in relation to the subject-matter to be amended as a consequence of such issues. This was the view taken by the board in T 127/85 (OJ 1989, 271), to which it added that it would be an abuse of opposition proceedings if the patent proprietor were allowed merely to tidy up and improve the disclosure by amendments not specifically necessitated by the grounds advanced for the opposition, even if those amendments were to comply with Art. 123 EPC. This applied equally to amendments during opposition proceedings intended merely to clarify ambiguities in the claims or description.
According to R. 81(3) EPC (R. 58(2) EPC 1973) limited consideration of amendments is intended to help expedite and streamline opposition proceedings (see e.g. T 406/86, OJ 1989, 302; see also T 24/88, T 324/89 and T 50/90). According to the established case law of the boards of appeal, Art. 84 EPC is an EPC requirement that has to be taken into account in opposition proceedings whenever the patent proprietor files any amendments. However, Art. 84 EPC is not itself a ground for opposition under Art. 100 EPC. Irrespective of how the granted claims are formulated, and be they dependent or independent, an opposition cannot be lodged on the basis that they lack clarity. Consequently, merely formal, syntactical reformulations of the claims do not give rise to a new objection outside Art. 100 EPC, i.e. under Art. 84 EPC (T 23/86, OJ 1987, 316; see further T 565/89, T 89/89, T 62/88, T 16/87, OJ 1992, 212, T 1835/08, T 1855/07, T 630/09). In T 792/95, another board confirmed the principle that, in opposition proceedings and subsequent appeal proceedings, only such amendments could be made as were necessary in the light of the grounds for opposition under Art. 100 EPC.
In T 113/86 the board of appeal followed this principle, ruling against the admissibility of amendments proposed by the patent proprietor which were not necessary to take account of the grounds for opposition invoked by the opponent under Art. 100 EPC or by the board under Art. 114 EPC, if there were the slightest possibility of a different interpretation being given to the patent specification before and after the amendments. The protection conferred by the patent would actually be extended if, as a result of amendments to clarify the granted claims, the claims could be more widely construed than a court would have construed them by the application of Art. 69 EPC. However, the board was of the opinion that the removal of an inconsistency between a claim and the description should be allowed if the inconsistency arose from an error, provided that the error was so obvious to a skilled person in the light of the patent specification as a whole that an interested third party could have anticipated the extent of protection conferred by the amended claim. In these circumstances the request for the correction of an error did not represent an abuse of opposition proceedings. Moreover, the removal of the discrepancy was in the interests of legal certainty.
However, where a deficiency results from a discrepancy between the description and the claim, lack of clarity in the invention's disclosure can be objected to because that requirement comes under Art. 83 EPC, not Art. 84 EPC, and may therefore be taken into consideration in opposition proceedings (see e.g. T 175/86).
In T 684/02 the board considered whether subject-matter which had been deleted during the examination procedure in order to avoid inconsistencies in the patent specification could be reinstated in subsequent opposition proceedings. Reference was made to the previous case law in T 1149/97 (OJ 2000, 259) and T 37/99, where the boards had concluded that the reinstatement of subject-matter which, in view of Art. 84 EPC 1973 and Art. Art. 69 EPC, had been deleted or indicated as no longer relating to the invention before grant in order to avoid inconsistencies in the patent specification should as a rule not be admissible under Art. 123(3) EPC after grant. Based on the reasons and considerations set out in the above decisions, the board stated that the particulars deleted from the patent application before grant and considered in the case at issue could not be reinstated with regard to Art. 123(3) EPC.