Based on how it behaved a few weeks ago when discovery services were down for so long, I think that once you've experienced a system / planet then your game will continue to use that name in your discovery list. I wasn't testing for this behavior specifically, though, so I could be mis-remembering.

I'd say the best way to avoid encountering previously discovered and named systems is to head out to places that aren't attractive to the crowds. The region around a galaxy center will have a higher density of discovered systems as players cram into the decreasing volume of space around the center. Also popular destinations will be the galactic poles and the eight extreme corners of any galaxy (as defined by their portal address coordinates). So, go to systems near the outer boundary and kind of "in the middle" of things.

Even better, get out of Euclid and go beyond the next galaxies in sequence; Hilbert and Eissentam are almost as popluated as Euclid. Once you're past Isdoraijung then things thin out considerably, although any lush galaxy will probably have more Travelers than its neighbors.

As long as you have bases or visited space stations in any galaxy, you can always return there through the teleport network. Caution: if you do start a journey down the chain of galaxies, always drop a base computer and claim it in every galaxy. You can delete that base later. But if you enter a new galaxy and then, for whatever reason, teleport out using a teleporter in your freighter then you won't have a teleport target in that new galaxy and you'll have to get back there the hard way.