Yes. The LAX stay was overnight. I was talking to ticket agents at YVR, who could only "explain" the duration limit, but now I see from the Wiki that overnight would have sunk my plan anyway. although the Wiki does state without a counter, "UA social media team (Twitter) wrote on August 16 (2017), "Any connection below 13 hours is always checked through to the final destination" in the context of being regardless of being an overnight connection or not."
Neither I, nor apparently, YVR ticket agents, were aware even of UA's bag check regulations, they would only go by a partial understanding and when the facts contravened that understanding, by what the bag tag printer spit out. I would hope the bag check software conforms to what's in the Wiki, because one would have no luck having these agents override anything.
I'm still sticking with next time, check them anyway and pick them up next morning for re-check. In my experience, LAX, in my case, will call to let you know your bags are in the baggage area unclaimed, but it will be interesting to see what their approach would be when they hear "sorry, I thought their routing would be the same as mine. I've left the airport now, I'll come back tomorrow AM and straighten it out." And I understand this is not a practical option for international itineraries into the US.
Nothing is more annoying than an organization, in the middle of an Irrops cluster, trucking out pointless,trivial rules to further worsen an already miserable travel experience.