The other thing to bear in mind is also that even from the factory from a good manufacturer there will be alterations - some basses leave with a shim on the neck - tolerance on CNC machines means that it won’t be perfect every time so a bit of pocket work is necessary. It’s no different in bitsa’s, you can switch a nut on a neck to have a reverse headstock whatever handed the bass is, pockets can be built up, necks can be shaved - as long as you keep your scale lengths correct, these minor tolerances are fixable, then the parts do fit