Not directly related, since my info is based on US.
I potentially have two separate PNRs ending/starting in DCA in two weeks, and there might only be a 1 hour connect between the two. This would not be enough time to claim/recheck a bag. I called US to ask about checking through. I was told that US used to do this, but now they really don't want to do it to reduce risk on their end. I was told that I might be able to convince the first check-in agent to do it, but that's not guaranteed. I expect I will book the second flight with a later departure and have a relaxed dinner at the airport in between instead.