So according to this information regarding the public availability of Sburb/Sgrub in human and troll societies/market, this means that headcanons where other children/humans entered the game and lived/are living their own adventures are plausible and supported by the official canon, whereas headcanons where other trolls (not included amongst the 24 we know) entered the game are not?

Nope, other trolls playing has no basis in canon. Although if you want to write a fanventure there are definitely ways around it. In a fanventure I was planning three years ago one of my trolls was supposed to play with Sollux but he booted him in preference for someone else after he sent the code and my old fantroll copied it and sent it to their friends and that was how they played.