I just realized that half of the systems I already visited have vanished from my discoveries list. I can still see them in the teleporter list, but when I travel there the name has reset to the game default and all planets including everything I scanned there are greyed out as it was my first visit. The station services however are not reset, so I can't get a second guild reward or buy the exosuit cargo slot again.
Is this a bug or is the systems/planet list actually limited? If so, renaming anything doesn't make much sense when it is onky a matter of time until all changes are canceled.
FYI: I am playing offline, so my discoveries do not get uploaded to the NMS servers.

EDIT: Is this probably related to the save file size that apparently doesn't exceed 3 MB?

Here some factors that I know about the entries in the Disco Page & Teleporter, this is info that I have observed since playing Foundation release. Note that the teleporter mechanics have had big changes in past versions.

- For a space station to be added in teleport, you must put your feet on the ground there otherwise it's not saved and you can't easily re-visit that system.
- The Disco Page will chronologically list all systems and planets if you have entered the system, wether you make discoveries or not, wether you visit space station or not, but it doesn't mean that you can re-visit those systems (see above).
- Only 70 space stations and 50 bases can be saved in teleporter No more bases are saved in the savegame. I guess the disco page also has a limit, but I cannot tell which one.
- In the past the NMS world has been reset; names in the Disco Page will change but no entries should get lost
- The updates made for the Disco Page since Beyond don't have any effect on existing entries, they just are displayed differently.

The Disco Page is not very useful to find systems together with the galaxy map, it's more useful to have an overview about fauna, flora and location discoveries done, although you can put a 'waypoint' by left-clicking on a system, but if this system is far away it will not show-up in the galaxy map, so it's rather futile, also because there is no way to tell how far a system is from your current location (this info has been removed with the latest version, distances were displayed in past versions.)

I hope this helps you, although maybe not directly answering your problem.

Unlikely. My main save game was started in one of the early 1.x versions and reached over 7 MB in version 2.15.
Although its size reduced to 3 MB with the 2.24 upgrade (not sure what happend there), it is now at 5 MB again after some extensive base building.