short version: when you have time, please archive (using Wayback Machine or similar) to archive artist userpage(s) in case they change username or shutdown the galleries we know about. (but the URLs e621 knows about linked to new gallery/galleries)
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So i wandered across artist spicymelow on e621,
but their e621 artist page ( https://e621.net/artists/60380 ) only has only ONE link (Twitter link) in URLs field
and that Twitter account link now results in "This account doesn’t exist".
I hoped i could see an archived version of artist's Twitter userpage to see if they had another galleries,
but it seemed neither Wayback Machine nor https://archive.today/ had archived artist's Twitter.
Turns out Wayback archived some tweets, but it wasn't obvious they had done so because no one archived Spicymelow's Twitter userpage ( https://twitter.com/Spicymelow ).
archived tweets: https://web.archive.org/web/*/https://twitter.com/spicymelow/*
Archive tweet URLs handy if artist has simply changed Twitter username (because twitter.com/OLDname/status/tweetNumber can forward to twitter.com/NEWname/status/tweetNumber ).
(nothing archived at:
https://archive.today/https://twitter.com/Spicymelow* )
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example of Wayback Machine in action: https://web.archive.org/web/*/https://twitter.com/rizonik_draw
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(wasn't sure which forum category was appropriate. Since archived finds could be used for artist wiki pages, putting in Tag/Wiki Projects category)
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EDIT: currently i just use
1) Wayback Machine (https://en.wikipedia.org/wiki/Wayback_Machine )
2) and archive.today (https://en.wikipedia.org/wiki/Archive.today ),
but more info at https://en.wikipedia.org/wiki/Web_archiving
and https://en.wikipedia.org/wiki/Category:Web_archiving_initiatives
Updated