The ATR-82 is one of the many ATR paper-planes that have not been built
(at least not up to today). The ATR 52 is in fact a military variant of
the 42 with a redesigned tail (loading ramp), but still has to find a
launch customer. The improved variant of the 72 is the 72-210
the ATR-52 has been a military variant of old ATR-42-100, built for italian Marines as cargo and EW aircraft, there was only one built and the project was cancelled.. I have a picture of it, but somewhere on Floppy, and digging it out will take a while...
and ATR-82 is a try to win the contract back and outfitting the ATR-72 this time with Cargo ramp and modified engines. I do not think that this airplane has ever been built, although there were some drawings of it....