I'm not sure if this has been debated and discussed; I know that everyone is aware that the 20% GCU discounted is limited to three per title per year (it's been debated it if is per platform or title (include SE/CE/LE).
However you could always buy more at the risk of getting blacklisted. Not sure if that has happened to anyone.
I don't keep a spreadsheet but I thought I was at or around three for FEF: Birthright and Conquest as I got a SE, a copy of each for myself and a copy of conquest for a friend.
I gave my original 3DS to my younger brother and went into BB to get him his own copy of conquest. I declined the $19.99 DLC add-on for birthright that was offered at the register and even after scanning my Best Buy Elite Plus membership ID the 20% discount did NOT apply.
I didn't argue, left with the game and went home.
My receipt clearly shows my best buy ID number but no discount. When I log into my bestbuy.com account it shows that i'm still GCU until 02/2018 and it's taken discounts off each game I add to my cart, including FEF Conquest. I did not check out.
I was wondering if maybe the "limit 3" is now or soon going to be hardcoded in the the point of sale systems? I have nothing to compare this too since I almost never run into this issue.
But as I mentioned as of now the website is still showing my GCU membership as active, I can still place orders (haven't tried a trade-in in a few months) and still have all my reward zone certificates in tact.
Edit: I did buy Doom a week or two ago in-store and GCU applied to that.