Midwest, cite your sources. If a person comes to us, tells us he is Jewish and keeps mitzvot we believe him unless there is reason to suspect him. See נאמנות אדם על יהדותו by הרב עקיבא כהנא.
In many European countries records go back a very long time. In fact, the Nazis ym”s would investigate a person’s lineage back 150 years before letting him into the SS. Today there are professionals who can trace a person’s ancestry using immigration and other records, both in the US and Europe.
As for your friend, how did the wife feel about converting and remarrying him? I know of cases of mixed marriages where this happened and in one case even attended the sheva berachot after their remarriage.