... though I'm more inclined to think that the balance that you saw might've been outdated.
This.
If the wallet has loaded "OK" (ie. Bitcoin Core didn't output any obvious errors with the wallet being corrupt) and there are transactions displayed, then I would also guess that the previous balance that was shown was either outdated, or there have been transactions since the last time the wallet was used.
Either way, I would expect that the current balance showing
now with the wallet file fully synchronized is correct.
I would also suggest that the OP should run an audit on all the displayed transactions and make sure they tally up with what they expect... hopefully it is just a case of a forgotten transaction, and not loss of funds due to the wallet being compromised.