... what do you think "to source something" means? It means to check the cited source for a claim. This is an incredibly common usage. Maybe it's more academic than I think it is?
Not wishing to add to the confusion, here, but to
me, "to source something" is to
establish (or present) the sources for facts (or 'facts') given by yourself, not to check those sources already cited by another in their own work, which it did bot seem obvious to me that you were asking to be reviewed (even though it would be a normal thing to ask).
But then it might be an Americanized/Anglicised divide thing. (Like asking to "write me"[1] instead of "write
to me", something similar compared to being "set on fire" that I can't currently recall your version of, or the famous problem with the term "to table [some issue or other]".)
(So, anyway, by that count the sources were already pre-sourced, as I take it, whether or not they were verified. And as I've not dove into this argument's specifics[3], I don't even know if/by how much even it was sourced
in that way, I'm just watching the arguments fly and (until now) keeping out of it. It being Not My Business.)
[1] To be written implies one is to be the subject of writings (e.g. to write a character into existence by authoring a novel with them in; or "write me sympathetically", one might implore of your biographer/ghost-autobiographer), not the object. In normal[2] Br.Eng usage, anyway.
[2] Nearly wrote "regular", despite definitely not meaning anything like "periodic"... But these things do keep creeping across the Atlantic!
[3] The only big point I would make is that clearly some people in the UK government have been striving to make the UK health-system more US-like (rolling back the whole social healthcare system by continuous interference and repolicying and effectively defunding it even while establishing more wasteful sinks to soak up all 'honest' funding increases that they can then use to try to debunk it). It makes me groan every time anyone (of any political colour) pushes for "healthcare reform", as often this is going to be hot on the heals of a prior (possible opposite-hued, but even ones that are nearly identical!) 'reform' that never even got the chance to settle down and establish its efficacy in solving the prior problem-of-the-week before being branded irrelevent/not-the-answer/counterproductive. That said, while I may have felt it best not to bother the doctor with an ailment (pre-Covid, never mind post-Covid/during) I have never felt that I
could not afford to do so (or not even afford to take a day off work, if applicable), and have not hit such limits of care that seem to be the one big issue for so many under the 'Merkin system... But this point is so often rehashed. And it seems almost as much "there's no simple way to get to <sensible system> from <current system>" as the other big issues[4], but
not actually so much if done sensibly.
[4] Like the old "Guns! Yahoo! Everybody and their dog has them!" being transitioned to one in which that's pretty much a negligable chance that most people need/have/desire a gun (police, honest citizens, even criminals... each group not having to contest with either/both of the other two groups being armed
by default, so "you go first" attitudes all round.