Puppy bites are tough, and I don't tend to get too worked up about them as they can go through all kinds of funky phases. Basically, I look to make sure that they're nice and wide, straight and sufficiently undershot at 8 weeks. After that, I don't look again until they're anywhere from 8 mos to 2 years.
One of mine's bite went "off" (wry) between 4 and 7 mos of age, only to come back at a year, another went very undershot, to the point of showing teeth with her mouth closed at 6 months only to come back at a year.
Bites change so much throughout the growing period that you really can't focus on them too much. As with many things structurally, however, your best insight is to look at 8 weeks and then not again until closer to adulthood.
Having said that, if a puppy is wry at 8 weeks, it's likely that they'll be horribly wry at 6 months and still wry (although somewhat improved from 6 months) in adulthood. Same with a puppy that is horribly undershot (to the extent of showing teeth) or level at 8 weeks and one that is overly narrow, etc.
Sometimes, however, puppies do have nice bites at 8 weeks that go off and never come back even into adulthood. . . Unfortunately, this is one of the bigger gambles that we take with purchasing show prospects as puppies.
