Wolf: In the absence of proof of mamzeirus (perhaps required to be made to a beis din), my understanding is any Jew maintains a chazaka of being kosher.
Furthermore, while Moshiach will reveal many things when he comes (such-and-such person is a Jew despite always having been sure he was a Gentile, such-and-such is a Kohen despite thinking he was a Yisroel, etc.), one thing Moshiach will not reveal is people who were assumed to be kosher but were in fact technically mamzeirim.