[password4321]

> if the signature and timestamp were fraudulently created

This is enough, independent of whether or not it happened after any of the certificates involved have expired. I don't think most consider total "key compromise" (of the 3rd party timestamping cert + the code signing cert) part of the threat model... but if there was an issue either could be revoked at a specific point in time. (Mentioning algorithm compromise takes away from your argument, when that happens entire segments of PKI get tossed.)

https://knowledge.digicert.com/generalinformation/INFO1119.h...

A user’s software can distinguish between code signed with an expired certificate that should not be trusted and code that was signed with a Certificate that was valid at the time the code was signed but which has subsequently expired.