In T 238/92 the board of appeal did not consider a document presented for the first time with the statement of grounds of appeal as "late-filed", since it served as the first evidence of a feature considered in the contested decision as essential for the assessment of inventive step (see also T 117/92). In T 1380/04 the submission of D16 along with the statement of grounds was a justified reaction to the opposition division's decision. The document also appeared prima facie more relevant to inventive step than any other document already in the proceedings (see also T 1146/06).
In T 666/09, the board agreed with the appellants that the comparative study filed with the statement of grounds of appeal was a direct response to the opposition division's decision.
In T 101/87 the board drew a distinction between (a) the case of an opponent attempting to find further prior art when the opposition division had decided that the original citations did not warrant revoking or restricting the patent, and (b) the case of an opponent making a further search in response to substantial amendments of a claim or to comments from the opposition division regarding a missing link in a chain of argument. In the latter case, new documents could be admitted into the proceedings, instead of being regarded as late-filed.
In T 927/04 the board stated that it was legitimate for a party who had lost in opposition proceedings to try to improve its position in appeal by filling a presumed missing link, as in the case in point, with respect to the issue of prior use.
In T 259/94 the appellants submitted new evidence two years after filing the appeal. The respondent did not object to their introduction into the appeal proceedings. The board held that in such circumstances the principle of "volenti non fit iniuria" empowered it to admit the late-filed evidence.
In T 828/14 the board examined whether the change in the line of attack was justified as a direct and objectively appropriate response to developments in the first-instance proceedings, and in particular to findings in the contested decision. The document was admitted into the proceedings.
In T 241/10 the board stated that the board has no power under Art. 12(4) RPBA 2007 to hold a document filed with the statement of grounds of appeal inadmissible if the filing of that document was a legitimate reaction to the submission of amended claims by the patent proprietor shortly before the first-instance oral proceedings and the opponent could not have been reasonably expected to present that document in the proceedings before the opposition division (similar to T 980/09).
In T 1817/15 the filing of E6 to E8 was regarded as a legitimate and appropriate reaction to the assessment of inventive step conducted in the decision under appeal for amended claim 1 in the sense of cases T 238/92, T 1146/06, T 295/08, T 406/09, T 828/14 and, above all, T 241/10 (based on an almost identical factual situation), with the aim of filling the gaps in the appellant's chain of argument by providing the missing evidence suggested by the decision under appeal.
In T 113/12 the document was cited in response to a claim amendment that was made at the oral proceedings before the opposition division. The amendment was based on subject matter from the description. The board found it inequitable not to allow the appellant to respond to such an unforeseeable new situation with a new document. Such a course of action would effectively tie the hands of the appellant in appeal to only base their arguments on previously cited documents, having first given the respondent a free hand to amend the claim based on the description at the last moment in opposition proceedings.