while trolls in the same bloodline sharing last names is convenient in stories where it needs to be made clear who’s related to who, I’m still convinced that the whole of a troll’s 6-6 moniker comes from lusus sounds, and as such two ‘related’ trolls would have completely different names if it weren’t homestuck (where Jane Crocker and Nanna have the same given name despite being raised by different parents).

what I think is a stronger idea is that this is the reason it’s a noble tradition to give yourself a title. when your name’s Abcdef Ghijkl, and your supposed ‘ancestor’ is called Mnopqr Stuvwx, it’s hard to make it clear that your identities match; unless there happen to be pictures available of this ancestor, then the only thing really publicly linking the two of you together is your sign, which, theoretically, you could share with hundreds of other trolls of your caste.

but when your ancestor swapped out the unmemorable Stuvwx for something really indicative of who they are in life and the legacy they’re going to lead, like, say, Mindfang, then not only is that easy for people to remember, and something that’s really gonna get recorded in history books, it’s easy to just take that title for yourself and make it really obvious that you’re the second Minfang.

lowbloods don’t need that; they know they’re only going to go down in history, if at all, as Rustblood #98523988, and that if they’re lucky enough to get more than a number jotted down in the factory catalogue, it’ll just be their hatchname scribbled in.