It is settled case law that a remittal to the department of first instance is especially desirable where a new citation puts maintenance of the patent at risk or admission of a new objection would result in its revocation. Any re-assessment of the case then necessary should normally be carried out at first instance (T 326/87, OJ 1992, 522; see also T 97/90, OJ 1993, 719; T 724/03; T 133/06).
The board in T 638/89 followed this line of argument and remitted the case to the opposition division after admitting late-filed but highly relevant documents.
But where an entirely new objection does not prejudice maintenance of the patent, the board can refuse to admit it or else admit it and decide against the opponent (T 97/90). In cases where an opponent has first cited a prior-art document at the appeal stage of opposition and the board considers it to be the closest prior art and so admissible but not such as to prejudice maintenance of the patent, it may itself examine and decide the matter (T 416/87, OJ 1990, 415).
That remittal is not automatic where the patent is at risk is shown by T 1060/96. Here the respondent had had one year to challenge consideration of a document submitted by the appellant (opponent) during the appeal procedure and one year prior to oral proceedings. Moreover, the document was technically very simple and merely reinforced the teaching of known documents. The board refused the respondent's request for remittal and revoked the patent.
In T 258/84 (OJ 1987, 119), the board found it necessary to consider late-filed citations on account of their considerable relevance. As a rule, this would have meant remitting the case to the department of first instance (here, the opposition division) so as not to deprive the respondent (proprietor) of a hearing at a first level of jurisdiction but it had not disputed the new citations' relevance or objected to their late submission, so the board could see no reason to do so and ultimately revoked the patent itself.