My understanding of “expunge” is that for all legal purposes, the thing never happened. It’s the closest thing to a Time Machine in the law.
There are some places, specifically in government, where you have to disclose even expunged cases. Even though it’s expunged, there’s still a folio somewhere. It’s government. Once they have data, they don’t get rid of it, even if they’re ordered to do so.
What if you shot a man in the back, spent two years in prison and on release found a technicality that got it overturned and expunged?