I see nothing inherently suspicious about the addition of new facts in a client's position. It may be that further investigation uncovered a new witness, that a new document was found, or something else changed. Now, you may have a right in discovery or cross-examination to ask why the story changed to see if there is anything suspicious here, but the fact that a new fact was added does not necessarily make the story suspect.
In any event, there is no law against the addition of facts at a subsequent hearing. About the only prinicple involved here is that a court may take steps to prevent unfair surprise at the hearing, to give the other side time to respond to the new facts. The court has wide discretion as to how to handle the surprise, however, and may decide that the surprise is sufficiently minor that the hearing can proceed as scheduled.