I did runs from 10 to 50 pairs with the same API, no problems whatsover. I am now using 30 pairs with it.
Actually, I'm using the same API generated 45+ days ago. Never got banned, just the same 422 and very very few 429.
I don't think this 17 pairs/API is a hard limit. Maybe a recommendation.
But bear in mind that the next release of GB should address this problems.