In code bases as big as Unreal Engine 4, you can easily remove as much as 10k lines of code and nobody will notice. It's not uncommon to have that much (and more!) dead code even. A single missing memcpy doesn't mean much, unless it's part of a hot code path.
All these rarely visited code path bugs matter in terms of security of course.
All these rarely visited code path bugs matter in terms of security of course.