I know nothing about showing. But I know that on most of the pedigrees I have, it's nice to have all the weights. I'm assuming this is the Senior weight. So.... when is that? How old are they when they are considered senior? A year?
Weight is usually listed on a pedigree when the rabbit makes Senior weight. That can be any time... normally After six months. Some young rabbits will Zoom and hit top weight at a young age... then as they mature actually drop back a bit in weight.
Here is a link to the ARBA site with information regarding registering rabbits..