Another data point for SJU:

I flew EWR-IAD-SJU-IAH-EWR yesterday on UA. I had 45 minutes scheduled in SJU, but a delay in IAD reduced that to 20 minutes. My inbound and outbound flights were one gate apart, so I walked into the terminal, made a 20 yard U-turn to the next gate, and walked right back onto another plane. I had boarding passes all the way through from online/mobile check-in.

Given the delay, the computer (or someone working behind the scenes) protected me on a next day itinerary of SJU-STT-EWR, but I didn't end up misconnecting (or getting stranded in SJU). This all worked out because SJU is in the US - had this been an international connection (between IAD-SJU and SJU-IAH), I wouldn't have made it (and presumably MCT would have prevented me from booking a 45 minute connection).

For the wiki link to this post, I'm considering this a transit and not a turnaround because I had boarding passes for my ongoing flight, and because I wasn't turning around to return to my origin.