In T 682/91 the board of appeal emphasised that a procedural violation which did not adversely affect the rights of the parties could not be considered substantial. The seriousness of a procedural violation derived from its adverse effects.
In J 14/99, as in J 15/99, J 21/98 (OJ 2000, 406), J 22/98 and J 6/99, it was decided that a procedural violation which had not played any part in the decision could not be considered substantial (see also T 2385/10). In T 2249/08 the board found it a requirement that the criticised discretionary decision of the department of first instance must be decisive for the outcome of the decision under appeal. In T 49/13 the board held that an error which would not have led to a different outcome of the proceedings was not a substantial procedural violation (see also T 1340/10, T 1740/06).
In T 5/81 (OJ 1982, 249) it was stated that an alleged violation affecting a part of the decision other than its ratio decidendi could not be a substantial violation within the meaning of R. 67 EPC 1973 (see also T 959/00).
In T 473/98 (OJ 2001, 231) the board held that the mere fact that the obiter dictum in the case in hand was somewhat misleadingly referred to in the pronouncement as "further decisions" in the decision proper did not constitute a substantial procedural violation. It was abundantly clear that no "additional decisions" were in fact made. The board further held that the inclusion of obiter dicta was entirely appropriate. See also T 725/05.
In T 712/97 the board held that the opposition division had considered the respondent's experimental report, but had not relied on it in a way adverse to the appellant. Therefore, the refusal to admit the appellant's experimental report into the proceedings, while a violation of the appellant's right to present comments on the respondent's experimental report, had no substantive effect on the outcome of the proceedings and did not amount to a substantial procedural violation.
In T 219/93 the board remitted the case to the department of first instance since it clearly called for revision under Art. 109 EPC 1973. The contested decision had also been inadequately reasoned on one point within the meaning of R. 68(2) EPC 1973. Nevertheless, the refusal had been made principally on other grounds, and the board did not consider the procedural violation to be so substantial within the meaning of R. 67 EPC 1973 that reimbursement of the appeal fee would be equitable.
In T 107/05 the board held that the opposition division's lack of consideration of the opponent's arguments on E5 had not been conclusive for the outcome of the appealed decision. The opposition division had considered E5 "acting of its own motion" and had assessed within its power of discretion that it was not relevant ‒ an analysis confirmed in the appeal proceedings. The mistake made by the opposition division could be regarded as a procedural violation but in this particular case not as a substantial one.
In T 1607/08 (see also T 2246/13) a procedural violation of the principle of the protection of legitimate expectation occurred. Since this violation led to the revocation of the patent and came as a surprise to the patent proprietor, it constituted a substantial procedural violation (see also T 1423/13). In T 2321/08, the examining division violated the procedure foreseen in Art. 94(3) EPC 2000 EPC. This procedural violation was considered substantial because its immediate consequence was the refusal of the application.