Purely speculation on my part, but the suit from Infinity War was based around having nanobots as confirmed here.
The suit was entirely contained in a detachable housing unit of nanoparticles which could deploy over Stark's body with a simple push on it.
I'm assuming that since the nanoparticles are so configurable based on Tony's thoughts, as seen when he produces all of the cool weapons from nowhere during the movie, MK 51 onward could reuse the same particles and just configure themselves differently. Suit designs 51 through 84 may have just reused the same nanoparticles that arranged themselves differently when activated, thus the other suit versions don't exist anymore because the same components make up MK 85.
The closest I can find to confirmation is this line, from a different page on the same Wiki.
It is a direct evolution of the Mark L, and as such, it functions with the same nanite technology, granting great versatility and efficiency.