That tail thing is mentioned in the Love's Corn Snake Manual - about looking at tails to sex snakes. They say it is one of the more reliable methods of sexing snakes and they have photos to show what they are talking about. They say once you get good at it, it is near 100%.
Problem is, I don't nessesarily think tails are a great way to sex a snake. And they have photos to back their claim, but I can't really tell from the photos what is male and what is female. Even though they describe what to look for, I couldn't tell what is what from the photo - except that they actually tell me which is male/female under the photo...
I tried comparing and looking at tails with my hatchling Cals and messed up on almost half of them after probing. Slightly better odds than just flipping a coin. Although it should be noted that I had no prior experience trying that method and 5 snakes doesn't nearly make a large enough sample. I've never learned how to pop, so I'll stick with probes...