We have noticed some pre-made frames being delivered/installed around our estate....but yes ours was assembled on-site.
I have to admit, our chippies have done a wonderful job so far.... no chipped or broken timber being used, no bottom plates or studs are hanging over the slab edge, and the site is still fairly clean too....
Allan, I'm sure all frames whether built on site or off site are within tolerances, regarding quality that is. I would hope anyway???
Well done chippies!!!