Something to note when comparing different armors is that the ratings systems are all independent of each other.
The NIJ rates armor with their IIA, II, IIIA, III, IV and "special threat" categories.
Only a piece of armor submitted to and evaluated by the NIJ gets one of these ratings.
(The NIJ being the "National Institute of Justice", these vests are typically law enforcement oriented)
The military uses its own system and standards for most (all?) of its armor.
Hence, the Interceptor and other military armor systems do not have an NIJ rating.
The military vests are built to meet the threats specified by the military, these threats and methods of testing do not necessarily line up with what the NIJ does.
Some manufacturers will submit their military vest to the NIJ and get a rating for it, then sell it on the LE market. Those military vests may have an NIJ rating. (I want to say that Paraclete did with their quick release vest, but I may be mistaken).
Bulletproofme offers both "mil spec" and "NIJ IIIA" versions of the Interceptor and according to their website, the IIIA version is thicker in order to meet the NIJ spec.
Also remember that the NIJ spec deals with back face deformation. I am not familiar with the military standards, but to meet the NIJ standards the deformation must be under a limit for each level.
(A level II vest may stop a 44mag, but it might break some ribs and cause major injury even in the event of a stop, the IIIA level limits the deformation to a less injuring degree)
ETA:
When you're looking at rifle plates, check if they are "in conjunction" or "stand alone".
The NIJ will issue "level III in-conjunction" or "level IV in conjunction" ratings for plates.
The "in conjunction" means that the plate meets the NIJ III or IV standard, but _ONLY_ when backed up with IIIA soft armor.
Don't put one of these in a plate carrier.