Most of the new rims that we get in my shop can be trued pretty darn close other than the seam. Sometimes I sand/file the seam smooth out of ocd. High performance wheels can get into the .001 or so range but even close to that is splitting hairs. If I get within .020 or .010" its usually good for most users. On my personal trail bike that uses discs, I really don't mind 1mm if the spokes are tensioned solid. Stability is far more important structurally than an imperceivable hop in a rock garden.