e621 has posts by an artist called pawsitively. I looked at their FA account (https://www.furaffinity.net/user/pawsitively) and it says that artist name represents a collaboration between two artists:

This account was a now-defunct collab project between artists lovespell + memento~mori

Both lovespell and memento~mori have their own separate artist pages here. The wiki page collaboration says: "Include all applicable artist tags to the image."

So, my question is: how does this affect tagging of the existing pawsitively images?

• Should all pawsitively images have the collaboration tag added? Because "collaboration" suggests that the two artists worked together on each image, but it's possible that they made them separately and just uploaded them to a shared FA account.
• Should these images have all three artist tags: pawsitively AND lovespell AND memento~mori?
• Should these images only tag the two artists, and the pawsitively tag be removed?
• If pawsitively is removed as an artist, should it be replaced with a set/pool to collect the images created under the name of that collaboration?

chemistrynoisy said:

• Should all pawsitively images have the collaboration tag added? Because "collaboration" suggests that the two artists worked together on each image, but it's possible that they made them separately and just uploaded them to a shared FA account.

No, you have already indicated the reason why it shouldn't.

• Should these images have all three artist tags: pawsitively AND lovespell AND memento~mori?

No, tag pawsitively as well as the artists you know were involved.
This involves checking each and every post they had uploaded and seeing if they mentioned in the description that it was a solo work.
If there were no mentions of any solo works, then you can tag all 3 artist tags.

• Should these images only tag the two artists, and the pawsitively tag be removed?

No, we tag both the individual artists as well as group accounts. Group artist tags should be tagged alongside the individual artists, but only the ones who were involved.

• If pawsitively is removed as an artist, should it be replaced with a set/pool to collect the images created under the name of that collaboration?

No, we generally don't do that unless it was a one-off collaboration project.

No, tag pawsitively as well as the artists you know were involved.
This involves checking each and every post they had uploaded and seeing if they mentioned in the description that it was a solo work.
If there were no mentions of any solo works, then you can tag all 3 artist tags.

Thanks. I haven't checked every image yet, but all the ones I've looked at so far on FA just say "Art © Me", with no explanation of which artist made which contributions.

chemistrynoisy said:
Thanks. I haven't checked every image yet, but all the ones I've looked at so far on FA just say "Art © Me", with no explanation of which artist made which contributions.

If it is signed off in the group's name (i.e., Art © pawsitively), then you can assume that both of the artists had worked on it.
What I meant about checking the descriptions is that, sometimes, one of the artist may have posted a tribute piece or solo work (e.g., "X drew this while Y gave me the idea." or "X have drew this as a little bonus art.").

However, since this is just a small 2-artist group, it is safe to assume most (if not all) of the artworks were worked on by the two artists.
Otherwise, they would have published separately on their own accounts (and would be tagged in that artist's name only).

You would encounter more distinctions in collaborations of 3 or more artists, more commonly seen in Japanese doujinshi groups/circles (see topic #30854).
It would be more common for one artist to work on a comic series solo while the other works on an entirely different series, and both of them publish under the group's name.