Experiment 1: I made a new save to do the latest expedition and I wanted to see if I could visit a base created with my previous save. I went to a system discovered by previous me where I had a base next to the portal. The base was not there. It appears that, even though your bases are always there even when you log off, if you switch to a different save they disappear. I did still have credit for discovering the system, though.
Experiment 2: You know how when you find a ship you like and you hang around until another of the same ship lands, it might be a little better or a little worse in terms of number of slots and/or core stats. I wanted to find out if I got the absolute best of a C class and upgraded it to an S, would it be the best possible S class of that ship. I found a solar I liked and found the best possible C class of that ship and flew it to the space station. After upgrading it S, it still a had good number of slots, but only middle-tier core stats. So, no, that didn't work.