I wouldn't call them 'bad' years...I get years where I am disappointed that a particular male did not want to breed. This year my 2 year old Banana Lesser male refused to mate with any female. It happens every now and then--usually they grow out of it...
If you want 1 clutch/year and you aren't picky about the genetics (which I am): You could assume that if you mate two males/female (all mature-of course) that one of the males would get the job done. Then it would be a reasonable expectation that if you have 1 female and she lays eggs in a particular year that she may not lay the next year...so that would be a minimum of 2 females. Now, if you are talking females that are unproven I would plan on an extra female just in case.
Final score: 2 Males: 3 Females for a reliable 1 clutch each year. The problem is: Project goals. Many times you will have only 1 mature male and female that can push your project forward as you would like.
In my experience females easily reach breeding weight, but, don't reach maturity until their 3rd winter. Some males can be ready to breed at a ridiculously young age/size. I'm always optimistic that a large female @2 years of age will lay eggs, but, so far I haven't had any luck.![]()