The game is so poorly balanced that anything is potentially an "exploit."
They do have a trigger where the old strat resources just become valueless...but it's incredibly late. I suspect it is when they literally cannot build any units that use those resources.
Exploit = something in the game mechanics, allow you to do something that clearly is not intended for you to do so. Shift-enter is such a exploit.
What is the shift-enter exploit?
Someone can probably describe it in better detail than what I can, but I understand it to be that you can get around the game trying to force you to pick a tech when you burn a great scientist or get a tech from a wonder or social policy by not clicking on the notification icon and instead pressing shift+enter to end your turn. I'm not entirely sure, but perhaps it's possible to have set up your tech path before hand so that when you finish your current tech, you aren't forced to choose a new one (and hence choose the free one).
Basically it can be abused to beeline expensive techs.
More specifically, you start the game, research writing, build GL, before it finishes click Civil Service in the tech tree, let GL finish, do all actions for your turn, hit Shift-enter. Repeat until you are actually teching Civil Service, then use the free tech you still have to take it.
This allows you to build the GL in a competitive time-frame while still getting silly stupid good use from its free tech.
I'll admit I used it when I totally spaced on stopping my oxford build in a game when I was going to use it to bulb the next tech in the line not the tech I was 2 turns from finishing![]()