The way I understood it in the movie was that no one knew where Luke had gone. Lor San Tekka is a kind of space archaeologist. Indiana Jones in the Star Wars galaxy if you will. Somewhere in his travels he’d procured this ancient map to the very first Jedi temple. When rumours emerged that Luke may have gone there, Leia contacted San Tekka to get the map fragment from him.

With regards to the full map, Kylo Ren says to Rey that the first order got it from the Empire’s data base but it is missing a fragment. My guess is that somewhere in history a Jedi or someone likeminded feared that the Empire would destroy the sacred site so infiltrated the Empire’s database and removed that section of the map so they couldn’t find it.

The resistance now have the fragment but are missing the larger map from which it was taken. Artoo however, is the missing part of the puzzle. Presumably, either when he had access to the Republic archives or when he was plugging into the Death Star’s database he was able to download the larger map and has been storing it since then.

I agree, there is a lot of speculation as to exactly how the key players got a hold of these different versions though. Maybe it will be one of those things we will be debating endlessly.

Looking forward to the forthcoming Raiders of the Lost Map to Ahctu : a Star Wars story.