Cmdr Molan Ryke suggested i take a look at this thread.
Nice finds, but i think you underestimate the numbers of PN in the galaxy.
Personally i have been visiting PN since i went looking for a Cereleum Storm Cloud NSP, which i dont think exists yet, or is codex bugged and doesnt spawn.
Been visiting PN for 1-2 years at least just looking for the storms. brings you across many examples. Many do look the same but over time many patterns and common features of their positioning. the 'starcubes' i call them, large B stars mostly, but also will include a few supergiant M,K and carbon stars.
Imo , not a bug those. massive stellar density with massive stars in a small region,often many BH and NS systems cluster around those areas. pulls things tight and dense.
PN just naturally occur it would seem around those.
You may of noticed Sapyx image 2 posts above.
They often are clustered like that. Certainly in the core and middle regions of the galaxy, further out and towards the edges, rarer to get clusters of PN.
just stellar density of the galactic regions overall. a lot more viable concentrations of stars across most of those regions, where they can form easier.
Not only stellar cubes, but large and medium nebulae can also cause that effect, having a sphere of PN around the nebula,usually 250-1000 lyrs radius around a large nebula.
similar size for a stellar cube cluster of PN, if you find one with a dense skybox, you should check around in galmap.
There are ways to find them, takes practice, patience , and time. i call it surfing galmap.
locate , bookmark, search area around that bookmark , add more.
normally i have clusters of 6-18 PN in each grouping, when in the inner 3 regions of the galaxy
must have visited well over a thousand PN now. maybe 1200 approx? and theres many more i have not visited yet.
takes time to search them out.
but there are virgin PN undiscovered out there. recon i have about 5 first discovery PN , so 5 in a thousand chance isnt bad
Many were partially discovered. like just the NS star , and missed 20 objects.
i shall have to get in game to check which bookmarks i currently have.
is there a record for smallest PN? think i may have it if so.
i thought i'd seen small PN before until i came across a cluster of 4 in the galactic core, 3 were all tagged up but the tiny little thing 35 lyrs away was missed totally.
iirc was only about 1klyr away from explorer's anchorage next to SaggyA
Best one i recon iirc was undiscovered PN with 80 objects.
i'll try dig out some info and add it here.