I've seen reports from people not being able to run more than 13 nvidia cards in one rig. Didn't try that many myself so can't say for sure, but those who tried it said that they could add more amd cards to that same rig (up to 19 cards in total), but not more nvidia cards (so the rig would work with 13 nvidia + 6 amd, but not with 14 nvidia cards).