My spouse and I have played NMS since release. After switching to the Steam version a number of years ago, we were lucky enough to start our current save in a system that had a paradise planet. While we weren't the first to discover the system, we were the first for the planets, flora, fauna and minerals.
Anyway, we both started bases on the paradise planet and have had those bases ever since. This planet was one of my favourites with gorgeous fields of glowing flowers (at night), purple grass, no storms, pretty water.... you get the picture.
When settlements came along, we moved our main bases to settlements, one of us on the paradise and the other on a toxic planet in the same system.
I spent many, many, many hours adding to my settlement, doing clever things to make it look nice and RPing the hell out of everything.
On the paradise planet I also turned my first base into a 'tourist attraction'. Then discovered this absolutely gorgeous flat field surrounded by hills. Inside one of the hills was a natural cave entrance. Low and behold the cave also looked spectacular with glowing fungi. So I also RP'd this as a tourist attraction - land in the field at night for a rolling field light show, enter the cave and go spelunking lit by cave roof covered in glowing fungi.....
Then the first planetary generation update came. All seemed well until I reached my 'Cave of Wonders'. The glowing fungi was gone. It was just a barren boring cave now. That hurt, but fine. It wasn't as bad as some people got as we still had a beautiful purple glowing paradise.
Then an update to settlements wrecked all my decoration. So I meticulously fixed it all and made it even better. I have cared for my settlement, made good choices for the inhabitants....
So, I was super looking forward to how beautiful our slice of paradise was going to look after the 5.0 update. I could only imagine how much more gorgeous the water and sky would look.
Imagine my horror when my spouse said that our main planet was showing as "Worm infested" when scanning. My anxiety rising I head to our paradise and my heart sinks as my ship clears the clouds. It is indeed now infested.
Worse is that my settlement is completely gone. The pin for it is still there but the settlement interface is non-existent.
All that remains is all the base parts I added - now either floating in the air or completely buried as the landscape has radically changed.
I then visited every single one of my other bases. Some are still functional as the landscape hasn't changed but the planetary type has in about 90% of them (weirdly some planets are still completely the same but most are different). My runaway mould farm has been replaced by metal fingers.
Worst off is our paradise planet where both the type and landscape are different.
There's other weirdness like the Discoveries being simultaneously reset but not - it will say a planet is undiscovered but when I land, it's suddenly gets the proper info back for it.
But on other systems, the discoveries are completely reset - in my AI Valve farm system, the system comes up as discovered by me but none of the planets were until I landed on them. The one that I have a base on has the name I gave it but all the other planets in the system are completely reset to their original names (and this system had some sentimental names as it was my final Atlas story system).
I'm going away for a week soon and was looking forward to playing some NMS beforehand. Now just have a sour taste in my mouth. So many hours lost and funnily enough I've lost any motivation to play at the moment. :(
While I do agree, there are steps that NMS could have done to allow people to keep their favorite settlements/planets. They could:
Only apply the new planet generation to undiscovered/new planets
Keep the old generation in a different "dimension" and allow players to view older dimensions
Only apply the new generation to planets that haven't had visitors/people there for X time.
Among other things. It's not an impossible problem, but it definitely would require quite a bit of extra work for Hello Games.
In all of those cases you are now locking away the new features to only be discovered at the ends of the galaxy or after beating the main game and learning about the multiverse. The galactic core would remain entirely unchanged. So everyone new playing would be stuck on v1.0 for hours until they get far enough away from EVERYONE while everyone else is drifting about in v10.4.
Look at Minecraft: if you keep your old world, you have to travel to places that have never been generated yet to see new chunks formed. Eventually you have a massive world where the center is old and buggy and then further out you go suddenly features are available. It's the reason why most people don't keep legacy maps running for years, and when they do, there's massive train/teleport systems in place to get you the fuck out of the og spawn.
They likely just have one algorithm that uses seed based on star systems id or location. This way the planets are the same for everyone and they only need to store data based on player interractions like bases and discoveries.
Due to this the changes can't be applied to just "selected" planets. Separate dimensions might be possible as they already have similar systems in place for expeditions and galaxies. These could however confuse returning players looking for new content.