If feature B depends on implementation of feature A, and feature A happens to be on the 20% wrong side, then feature B will be wrong too, regardless of whether you happen to have better luck with it being implemented on the 80% right side. It'll simply be built on a broken foundation. It WOULD have been correct if the foundation was right, but it wasn't.
This is actually very common in software development, where you rarely have stuff happening in isolation. A lot of features deliberately touch each other, build on top of each other, and even more so when you factor in "accidential" overlap due to unclean technical boundaries (in spaghetti code, everything touches everything).
Ask it to interview you before you start and it'll get your constraints pretty well.