Woudn't game share do a "trick" there ? I sold my PS4 like year and a half, but most of the games I never bought on my primary trophy hunting account, I always had separated accounts for bundles and frenchises so I can sell them further in my local community when I finish them. I can only assume that might be the thing for your question.
For some games, when you buy a game, you also get the other versions of the game at the same time, yes?
Some developers took that to the next level by also giving you every regions version of the game as well, each with it's own trophy list and a single save option.
So if the game in question is on PS4, PS3 and Vita, and in three regions, that's 9 platinums, with single save making 8 of them instant unlock.
You just need to have your accounts/systems set up to download from other regions.
A lot of these piles of platinums you're seeing are from Ratalaika Games.