No one I know has ever played with such a limit, especially because it really comes down to chipping up vs having the individual pieces crowd the board. Germany does not have enough tanks to complete most games of G40, and there aren’t even enough tanks included with the 2nd ed set to support Oztea’s G41 setup certainly not enough to support YG/Garg’s Deluxe setup without custom pieces or multiple copies of the game. We often use French pieces as proxies before the combat phase, after casualties the situation usually doesnt require they stay on the board.
One recommendation is to buy another set of chips, we have blue or pink chips to represent 2s and a few yellow chips for 10. Since factories produce 3 units and there are plenty of static 3 stacks in the setup, these chips add another level of convenience (so you have 1,2,3,5,10).
I know you want a citation, but except what you are saying about Classic, I have not heard of such a limitation. 1941, WW1, Ikusa all have far too few pieces included in the box to play a normal game, so it would be irrational to assume that the piece sets included act as limits.
Where is the “YG/Garg” set up information? Don’t know that ive ever seen it.