They're never going to be millimetre perfect.What I mean is that the bases are all then guaranteed to be level, then get the fronts square to each other and screw together. It is too easy to get separate feet not quite square, when it is one long run for the front and one long run for the back then they must be right. but going on Johnny2007's description some of the carcass manufacturers seem a bit sloppy.
Your ones seem out by a couple of mm.
Very acceptable.