On my most recent flight with my wife, we were waitlisted for mileage upgrades both ways. At the 24 hour mark checkin, I answered yes to joining the upgrade standby list. This automatically split our records, with no agent intervention. There was a single locator before, and two new locators after.

This would have surprised me had I not phoned first to get coaching on what would happen. My non-elite wife was Plat for purposes of this flight, because I was attempting to upgrade her with miles. We listed #1, #2, but did not clear.

On the 7am Sunday transcon return, the first cabin was 3/20. I removed my mileage upgrade request, but left my wife's alone. (I did not first to be already full when we would finally be able to request a companion upgrade.) She cleared about 36 hours out, and I cleared about 23 hours out, in time to arrange seats together before everyone else cleared.