Not saying you're wrong, but faithful hardware emulation is really hard. The VICE team are still working hard on perfecting a Commodore 64 emulator and recently completed their implementation of the VSP bug, which has been discussed elsewhere here on HN[0].
But that mostly means it wasn't ok (as in not faithfully emulating the hw bug) to begin with, and that it was super hard to fix, not that the VICE code rot'ed over time.
[0] https://news.ycombinator.com/item?id=5314959