The JW youth of today know how to hide what they are up to, and they protect eachother.
One example, I know a young JW who was hauled before a J.C as a witness, he was the only one who could say, for sure, that a certain unmarried couple had spent the night together, they had, but he told the J.C they had not. Where is the Holy Spirit when you need it, Elders ?
They tightened up the rules in about 1967/8 as has been said, so that even "Heavy Petting" as they called it, LOL, was condemned, before that just penetration was the no no, we had lots of non-penetrative fun in those days !