I first bought MS Office 365 Personal (Genuine from MS) and two years subscription cards add-on a couple of years back. I was getting near end of "limit" so I bought several "add-on" subscription cards (Genuine Microsoft) Scratch off, and started ADDING them to my MS Account. I reached "Expires 1/ 2022" and it STOPPED accepting any more legit cards. By the way, bought these genuine Microsoft Cards (Sealed) for $20 each !! NOT eBay Key-Gen crap.

I called Microsoft Tech. Support. Subscriptions (under same account) can only be stacked FIVE YEARS MAX.

I have TWO extra cards left, just don't want to lose them. Will use one next year and one year after that.