As long as the MB is linked to your
MDE account you are good to go, no matter when it was obtained or last used it. If it's real old, like maybe 3 or 4 years, it's possible you might not get ride photos but otherwise, it will work for everything else. I have had to have a CM at the front desk of a resort reset mine for some reason but that doesn't happen often nor does it happen with every MB. I have them all the way back to when they were first testing them with just a few resorts and all of them will get me in my room and into a park. I rarely look at ride photos so I'm not sure how my oldest ones work for that and I don't charge to them but from what I understand, even the oldest ones will work for that.
As far as a shortage, only the nonMB+s are in short supply. If you want the new ones, you can find those everywhere.