That depends on what the buying and selling club agree, every deal is different and Celtic were in a very strong position to include sell on clause the immediate and the next transfer. I seriously doubt we are in that position with anyone, and the fact the Penner's left livi at the end of his contract would mean in previous circumstances we'd have got nada as you can't enforce an agreement onto his next club, or club after that.
Thankfully the current system allows a bit more flexibility to reward the developing club.
If for j low was to move on for a few at the end of this season, we'd get that transfer fee as he's under contract, the end of the season after we could get no transfer fee unless he signs a new contract but there would be a development fee due to his age.
but as I understand it the thistle academy and also his previous club (as he had only been in the academy a few years) would get a payment as well.
Could be wrong, and happy to be corrected by someone that knows more about the current transfer system but that's my understanding