§1. If the respondent appears at the trial later or responds before a decision in the case, the respondent can offer conclusions and proofs, without prejudice to the prescript of can. 1600; the judge, however, is to take care that the trial is not prolonged intentionally through longer and unnecessary delays.
§2. Even if the respondent did not appear or respond before a decision in the case, the respondent can use challenges against the sentence; if the respondent proves that there was a legitimate impediment for being detained and there was no personal fault in its not being made known beforehand, the respondent can use a complaint of nullity.
Source: Code of Canon Law (Vatican.va)