A couple things I'm going to add to this:
Not too long after Matara debuted, she went down the 40K rabbit-hole and started collabing with Bricky, a twitch streamer who has done a lot of Warhammer stuff and is a
normie 3 view who occasionally hits 4 view status. She got quite a few extra followers when she started the Warhammer stuff and some of those usernames have stuck around. These guys were not necessarily vtuber fans at first and found her through the twitch warhammer pipeline, so that's likely a good chunk of that extra 600.
Another thing to note here is that Matara's CCV
halved after her first month back, and stagnated for the three months following that. Obviously some lost viewership was to be expected after the honeymoon period was over, but speaking as a fairly big fan of Nina, I got tired of V-shojo's terrible collabs (Henya is great, but Zentreya is just the worst collab partner it causes me physical pain to see Matara try to improv off of him and have to wait 5 minutes for a response). Twitch's constant shittiness as a platform doesn't help either, and I've just been tuning in less and less because of it. Her viewers went up a bit after she came back from break but given that Niji is such a hot topic right now that's to be expected.
So yeah, I'm actually not too sure that many of her old regulars made the jump over. And those who did, in my personal experience, are getting filtered out somewhat over time and replaced with V-shojo/Twitch viewers, for better or worse. The whales have stuck around but mannn I just don't know.