Wendy, I think you may have answered your own question;
Not every female will go every year. It is very rare to find females that will lay every season. I have one female (out of roughly 60 breeder females) that has given me eggs (7-11) for seven consecutive seasons but most will go a season, take a season off or go two season and then take a season off."Last year she laid nine huge fertile eggs for me... "