cbn42, your post piqued my curiosity about what exactly is going on underground at SFO once you check a bag. Turns out SFO has been very busy revamping the system in the last few years:

"We are the first U.S. airport to introduce the individual carrier system or ICS for baggage handling. It ensures that the bags remain in a single transport tote from drop off to cargo load in," he said.
How SFO Airport's Digital Revolution Transformed Air Travel
https://www.cio.inc/how-sfo-airports...travel-a-23873

Here's a video of the new individual carrier system (ICS) in action at SFO:
And I found this from a 2016 proposal to build the ICS:



Of course I don't have any real knowledge of how this system works, but it looks to me from the proposal that the International Terminal bag-check stations are very much integrated with all of the their domestic terminal counterparts.