Correct. Because it's in the original cryovac and not exposed to air, that item (usually the large/whole meats like brisket, standing rib) would work.
Key is duration. There IS an absolute date. And many competition cooks tend to go out 30 to 50 days. Most of what I've seen written say 21 to 28 is optimum.
That date is measured from the kill date and when you walk in the store, if the package is in the display case, you won't know the kill date.
Usually (not always) the "sell by" date is an arbitrary date that butcher fixes to selling the beef. Usually two weeks or less. If you go with that as a basis, then take that into account.
I've safely wet age stuff out of the case, but I never push it out past 21 to 28 days.
For the long aging, I won't go there if I don't know the kill date.
Now, that being said.
The temp inside the fridge is important. If it's constantly fluctuating (like your home fridge) that actually reduces the total duration. As explained to me, every time the meat is above 40, it affects the TOTAL duration.
Control the environment if you can.
If you can't, maybe only wet age for a week or two max.