I obviously don't know if this applies for the Fil-C bugs but what we saw in Rust is that there's plenty of "technically that's not OK" which is very distant from "this will actually cause real world problems" https://forge-blog.github.io/posts/rust-std-memory-safety/

For example it's definitely not OK that you can impl Pattern in a way that causes non-UTF8 data in a string with safe code. But you probably didn't let random attackers impl Pattern, on a nightly Rust where that's even possible, and so that's not going to cause problems in our real world - even though it's wrong and must be fixed.