Its two separate bookings indeed. Good to hear its still possible. What do you mean by record locators? PNR? So that and ticket numbers, got it! Last time I messed up because the name was slightly different in the two bookings and so that didnt work. This time its the same name. Should I reference to their webpage if they say it cant be done? Maybe not neccessary.
Record locator = PNR indeed.
I used to take along a PDF of the website page that covered the policy and had the Star file number UA had for such situations, but UA agents even at small outstations across the US know the policy with checking in bags across tickets and have made it work without me needing to document the policy for them over at least the last several years of my doing this a lot.
Same names and name arrangement on each of the ticketed PNRs is indeed very helpful to make it work.