The saddest story I've ever heard in that regard, was one told by Surplus about a friend of his at Comair. Seems a long-time Captain at Comair with many, many years of seniority was caught up in a drug thing as a younger man and helped the government in exchange for the arrest "being sealed".
Sure enough ... post 9/11 his stuff was flagged somehow and they found it pretty quickly. All those years right down the tubes. At least the two guys I talked to got caught while in ground school, so it wasn't as big a loss as a long-time career (though they probably didnt see it that way). In all three cases, their records were expunged or otherwise sealed, but their respective airlines found out in the normal course of post 9/11 record checks. Those are just three that I know of, so I'd imagine there have been many, many more.
My advice, the same advice I follow myself, is tell the truth and let the chips fall where they may. If it says "Have you ever been arrested ...", it isn't saying "this week". If it asks "Have you ever been convicted ..." it doesn't say "and not had the conviction overturned or otherwise sealed." It says what it says and if you don't want to get your heart broken in ground school you better tell 'em the whole truth, and nothing but the truth.
And then there was the idiot in a town near me who didn't list an old drug conviction on his student pilot medical. He caught a six month
ACTIVE sentence in a Federal penetentiary from the judge. They ain't playing, folks.