The Fleet Site 'Mainline Fleet/Future321' tab and 'UA Fleet Deliveries' page list Airbus MSN 12056 as being both N14524 and N14527, with N14524 starting test flights from BFM. According to other sites MSN 12056 will be N14527, and MSN 12061 will be N14524.

MSN 12056 (test tail F-WZMT):
https://aviation.flights/aib/A320/12056
https://xfw-spotter.blogspot.com/search?q=12056
https://www.planespotters.net/airframe/airbus-a321neo-n14527-united-airlines/rzmzgv
https://www.flightaware.com/live/flight/FWZMT

MSN 12061 (will be test tail F-WWSL out of TLS):
https://aviation.flights/aib/A320/12061
(The photo on the above page is crappy, but you can just make out the first three digits of the MSN a bit to the right of the yellow thing and the top of the fourth digit cannot be a 5)
https://www.planespotters.net/airfra...irlines/r7121y