I thought they have to be either pop or probed to determine sex i never read or heard anything about determining sex by tail length , thats pretty cool and seem way more humane but i bet its less accurate.
Good luck with sexing your new corn snake though
As a rule yes females have longer tails but as everyone knows exceptions to every rule it kinda give a hint as to the sex not 100 percent accurate although I havent been wrong yet w my corns by guessing first and then popping to see after