This 40ly range thing is actually a myth, (I assume, since...) for me they work across the galaxy.
Pretty sure that
was how it was working for me.
On day 1 the filter flat-out wasn't working
at all.
I'd visited 3 or 4 MTs (on the live server, not beta) so I definitely knew where they were but the systems didn't change colour in the galmap.
At the time, the "explanation" for this seemed to be "Well, they only show up once you've stumbled across them for the first time" - which is nuts, but there we are.
After 4 or 5 days INARA had about 40 MTs in it's list and I decided I'd visit all of them to ensure they
would appear on my map.
I got around about 20 of them but then noticed that the ones I
hadn't visited had started to be highlighted on the map as well.
At that point, the "explanation" changed to "They show up as long as they're at a station you've visited at any point in the past"
At roughly that point, it
did seem like they were
all showing up for me.
I could just scroll around the map then click on the filter and the systems would change colour.
A few days later, I noticed this wasn't happening any more and they were only showing up as I got within 40Ly of them - which, unless I'm mistaken, was how FDev intended for it to work.
On a related note, it beats me why the filter only applies when you actually hover the cursor over it, rather than working the same way every other filter on the map works.
If I want to find particular classes of star, or particular types of economy, I can just access the relevant filter, make one or more selections and then scroll around the map, seeing the matching systems.
Due to the way the MT filter works, I've got to scroll around the map, access the filter and hover the mouse over the selection and see if any matches appear on the map.
Quite why they couldn't make the MT filter work the same way as other filters is anybody's guess.
Actually, no.
I'm pretty sure the reason it's coded that way is simply to make it more fiddly to use.