When to use Manebooru Exclusive tag

Hi, I'm uploading some art from a friend who deleted all their pony accounts. They left the fandom and don't want to be involved with it in any way, but I do have permission to post their art related to my characters/stories on boorus, and I decided to make Manebooru the home for all art related to my stories (so long as I have artist permission).

Anyway, the description for the Manebooru Original tag says it should be used when a piece of art is posted to Manebooru first. This art was previously posted to Tumblr, but that Tumblr has been deleted. Would it be appropriate to use the Manebooru Original tag, as this is the only site the art will be on, or should I omit the tag because I'm not the artist and it was previously uploaded elsewhere? And if I omit the tag, what's the correct way to do it? Dead source, perhaps?

@Krickis

You can add Manebooru Original, yeah. If not entirely accurate it seems appropriate, and the team is okay with it. Dead Source is not needed, you (your upload) will simply become the source.

This is what makes sense to us. If it becomes a problem we will reevaluate but for now you can proceed with that guideline.

@Wcctnoam
Alrighty, thank you!