>What if somewhere, deep down in the stack there is an ancient bug that dented all of this?

Science is built on libraries with experience, that have been validated extensively against reality. Code often written by people who have retired and died because that exact same code has been validated and pinned to reality for decades. It is of course possible that a load bearing bug survives for a long time conspiring with an incorrect model of reality to give validated results, but wide use tends to eliminate these things.