I remember once I answered a question, and one of the sources I cited was Charles Oman's Art of War in the Middle Ages, and I thought "I'm not sure how I feel about citing century-old scholarship which has only held up partially under later scrutiny."
I'm wondering: are there any particular sources that you see used to answer a fair amount on this subreddit that make you think "Why are people still citing this? Its central thesis was refuted in the 1970s (or whatever)," or "Why do people ever cite this? It was fraudulent / sloppy from the start," or any other ways in which sources can be bad?
(Is Oman a good example of a bad source?)
I'm wondering: are there any particular sources that you see used to answer a fair amount on this subreddit that make you think "Why are people still citing this? Its central thesis was refuted in the 1970s (or whatever),"
All. The. Time.
Most of us are not idle on the subject. The thing with sources are, they can and often will be open to scrutiny; there's often wiggle room. There are some sources however that have just been plain debunked or are flat out assinine and should not be cited.
I'm a military flair, so I can't answer your question about Oman, but I'll give a few examples of Citations that get immediately reported by me for the reasons of them being outdated or questionable:
Anything from Dan Carlin. ANYTHING.
I often view Max Hastings in a critical light when he's being cited outside the realm of WWII; and here's why - he's a journalist first. The only reason I accept his citations for WWII is largely because what he states is either (a) common knowledge or (b) propped up or supported by his contemporaries and later publications.
Generally, anything written about WWII before 1970 is immediately and categorically open to scrutiny. Its either blatant jingoism, or barely concealed apologism during this period; and is often based more on interviews with veterans than it is actual army records. One of the most glaring examples of this I have ever read was a book on the Falaise pocket; published by a Frenchman in 1968. It had glaring inaccuracies and was filled with political messages and presentism more relevant to the burgeoning EU then actual events in 1944.
I actually once asked a historian about the infamous (or rather it used to be on the internet) Roman Circus and whether or not they actually did have a hundred little girls being raped by a horde of baboons.
He instantly knew what I was talking about (apparently it came from a book called 'The Prostitute in Society') and that it came from a book on human sexuality in the sixties and was not a credible historical reference.
People have mercifully stopped citing Gibbon. But some unreliable, tendentious recent work that gets cited, in my area, would be anything by Robin Lane Fox (his claims consistently boil down to "this is what I believe" and rely on ignoring anything inconvenient) or Victor Davis Hanson (more a political propagandist than a historian).
As for older material that is simply irrelevant: the worst offenders would be the writers on mythology. Joseph Campbell, Müller/Lang/Frazer/Harrison, Gilbert Murray, Mircea Eliade. Jakobson and Lévi-Strauss still have their uses, though. And Nilsson still deserves respect, even if he's obsolete. References to Robert Graves, however, need to be dropped in a volcano -- you might as well cite Velikovsky.
And I have mixed feelings about Moses Finley on the Greek Dark Age. His World of Odysseus was ground-breaking and important in its time, but it's obsolete now. I can see a case for recommending it for further reading, if more recent stuff is inaccessible, but never for citing it as an authoritative treatment.