I got my first white belt with my first gi. It was a fit (I guess) and I did not pay much attention to it. Gi was Tatami (size A2) so probably the belt was also A2.
I got another white belt with Ippon gi, A2 again. As our BTT gis come without belts then I left it on the hanger in the gym so that someone else could use it. And, it found its new owner quickly. Third one I got with Progress gi, A1L this time.