Upper receiver lapping?

[redhat]

I believe most uppers are cast and not lapped before assembly for mass production guns or complete uppers that most companies offer. I would suggest canceling that item and ordering it through another vender that has it on the shelf. Amazon has them and you can have it in a couple of days

Do we have (or should we try to develop) a list of manufacturers whose uppers were good/true out of the box and whose improved after lapping? (specifically in my mind, BCM, but curious about others). Just curious which uppers are most likely to benefit from this vs which are a waste of time. (This might be more appropriate as a separate thread)