They all grow differently. There really is no normal when it comes to BPs. Some are better eaters than others. I have a female normal that went from 870g in March to she is now sitting at 1800g on empty. But I also have a female that was 250g in April and she is only 340g now.

When you weigh them will also make a difference. If you weigh them after they have just eaten your weight won't be considered an empty weight or as close to the actual weight of just the snake. The best time usually to get an empty weight is if you don't feed while they are in shed and wait until after they have shed and pooped to weigh them. That is as close to empty as most ever are.