As these are hand crafted/placed assets I would not expect that many to be in the game. With the new scanners they are easier to find so most have been found.
I guess you're right on this. Also, the game has a history of things being "discovered" rather quickly. The best example was the story of some Thargoid content, which was found merely hours after the patch went life. The players claimed that they found the position by looking at the videos of the the presentation, spotting constellations and calculating the position out of that. It turned out, that the position where they found the Thargoid content and the position of the video did not match up at all. It wasn't even close.
Similarily, a lot of people "accidentally" stumbled over the generation ships merely hours after they were patched into the game. It's quite astonishing how many people at that time seemed to fly for one or another hour straight into the black towards no known destination for the mere fun of it, to then be surprised with a generation ship crossing their way.
One could almost think that somebody actually was datamining the patch for new content, figuring out the system and coordinates of the new things, then flying there.