Don't let not making the calendar a year or two keep you from submitting. I submitted pictures a couple of years before I had any that made the calendar. I've had pictures I submitted in the past end up in their catalog.
It's hard to sometime understand what they may be looking for. You have some fabulous pictures. I'd bet yours have been close to making it before they decided on their final 15.
I've allways been kinda suprised by the pics that I have submited that I have gotten into the calendar. There are some really good ones that I have submited that haven't been put in there, but ya know it's all about what they think looks good then.