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and there are transactions displayed, then I would also guess that the previous balance that was shown was either outdated, or there have been transactions since the last time the wallet was used.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.