Today’s EPROM is a very rare early prototype from MME (VEB MikroElektronik “Karl Marx” Erfurt ). Part of the East German state-owned electronics business. MME (and their predecessor FWE) made clones of Intel 1702, 2708-2764 EPROMs as well as many processors. These were all unlicensed, reverse engineered, or copied via industrial espionage since this was all before the end of the USSR, and the technology blockade put in place to ‘prevent’ Eastern Europe from using Western technologies. This particular U552D is a clone of an Intel 1702A, however, it is made in a plastic package (with what appears to be a actual quartz window). A very unusual package that was used in Soviet devices mainly and very rarely in the west.
The only western EPROM I have found in plastic is a prototype TMX2532-35NL from Texas Instruments (thus the TMX prefix).
However, the MME U552D actually has the window glued to the top of the plastic package, rather then integrated into it like the TI, and the Soviet designs.