As I said, I don't know how they calculate "sell by" right now (have notes somewhere at home) hopefully someone else can chime in.
What were you looking at, beef or pork or chicken?
Beef has a longer sell by date, but pork/chicken have substantially less. I wouldn't buy any pork that was more than a few weeks, maybe 2 at most.
Problem is that on pork/chicken they will store them around 28 degrees and according to the USDA, that's "fresh" not frozen.
If you're buying anything a month old, I wouldn't without know who you're buying from.
Inspect the meat and see what it looks like, check the cryoseal, the look of it.