I candle them. Hold a light up to them and if they are pinkish and veiny usually means they are fertile. If they are yellow them generally they are not fertile. Plus, only days after they laid they have started to colapse.
That's a bummer, but as you said, there are a lot of positives. Those are some beautiful snakes. I'm thinking my next snake might be an old world rat snake of some sort. Thanks for sharing.