I have just talked to the devs about this.
The number of bases is in fact limited to 21 bases, which means 1 starting base and 20 researched bases. The devs don´t want to implement the ability to research more, because there is actually no need to have more bases than that and it would make specific players too powerful.
I have also asked, if it was like that just from the beginning, and they told me, that it was like that right from the start of the game. So, i was in fact wrong, when i said, that they were unlimited and i apologize for that and any inconvenience this might have caused. Sad
Man kann nur 20 Basen erforschen + die erste Basis macht das 21 Basen. Grund: Spieler würden zu stark werden. Die zu Anfang des Spiels rausgegebene Information es gäbe unendlich war falsch, sie waren schon von Anfang an limitiert.