Mysterious_Uploader said:
It could be useful to differentiate between official and "unofficial" art, or at least art made outside of Arknights's scope. I think tagging pre-arknights artworks with the character tag could definitely cause confusion. (Throwback to the time post #2669457 was uploaded and was tagged as drawn by ZUN, making news circulate about an official Gensokyo map.)
That's a completely different situation, though. That was a fan creating and uploading something with zero input from the original creator, and a series of mistags confusing people as to who actually created it. It was never official or in anyway related to Zun.
This issue with Kal'tsit is a character that was created prior to Arknights, but was then coopted into the game during development. She was made by the official artist, she shares the same name, the same Familiar(Mon5tr), and despite some changes in appearance is still physically recognizable as the character she is now.
There is no confusion of who made the art, it's the same artist, it's just an old design, the fact she at one point appeared ingame with the familiar could mean the artist originally pitched the PF design and the devs accepted it, which would technically make it official, despite her appearance having been altered since then.
I don't see any problem with tagging it kal'tsit but not arknights if people feel maintaining the distinction is important, but then I could see people constantly adding the arknights tag and/or removing the pixiv fantasia tag, in which case I would suggest renaming Kal'tsit to Kal'tsit_(arknights) and tagging the pre-arknights version as kal'tsit_(pixiv_fantasia).
I think there's gonna be confusion no matter what you do, but at least with separate tags the wikis can provide clarity.