Yesterday. It worked when I went to pro about 6 months ago too and I didn't realize it, so I figured when I upgraded to Elite I'd just see if that worked, and go figure, it did. We didn't try with any more but my guess is if it worked for 2 stacks, it'll work for as much as you can pay for.
This would be REALLY good for the 50% trade bonuses going on, as you're only paying about 86 for 3 brand new games or high valued switch titles, and trade in for those 3 at 45 a piece (elite+bonus) would be 135.
Awesome, it worked 6 months ago for me as well when i renewed pro (4 stacks of 3) but did not a few months ago when i upgraded to elite (tried 2 stacks of 3 to test)
I will make sure to try again the next time just in case