A $5 MRE is probably 3-4 years old before you get it or they are MRE lite.
No, I spent many years in the .mil, so I know the “real deal”.
IF they are stored correctly they last a long time. For nostalgia’s sake I bought a half dozen of 1987 brown bag specials - and ate them last month for lunches.
Everything was just fine (well, as “fine” as they are to begin with) with the exception of the Kool-aid beverage base, it was no longer free flowing powder. Even so, the kool-aid would still be usable if necessary, just a bit of hassle.