A bit odd perhaps, at least Ii haven't run into this.
Planets in uncharted systems have no structures. However if you use a portal to travel to a planet in an uncharted system, a Portal will generate. I spent a good deal of time trying to portal to this world, and some other worlds in the same system. I've double-checked the glyphs several times. In all cases I get the address error, approximating. I'll end up in a different system around the same distance from the core every time.
I swear I've done this to generate a portal on uncharted worlds before. Did I not have enough coffee today? Has this been "patched"? As it is I portalled to a bunch of other systems anyways, so got a functional portal base for this galaxy. On to the next.
Glyphs 3207-FA00-6FFA
There are limitations to the algorithm.
Some systems are invalid portal targets. It's an infinitesimally small quantity, compared to the size of a galaxy. And it's a known thing.
TIL! Well, I guess my galaxy transit was delayed by a valid rarity! Well, I plunked down a base there, so I'll consider it an addition to my collection of rarities.