I currently have 3 Garmin devices that all have a Vo2Max function. Through the summer is was primarily using a 735 and my Vo2Max was a steady 53, but one day the battery was low when I wanted to go for a run. So I put it on a charger and pulled out my backup 235 which hadn't been used in a while and when I finished it gave a Vo2Max 49 and that became my official score in GC although it went right back after the next time I used the 735. Then yesterday I bought a Vivoactive 3 and took it for its first run so now my Vo2Max on GC is 48.
If the idea is to have Connect be the master source of your stats and things like alarms that are set on the watch can be overwritten by syncing with GC why can't Vo2Max be consistent across devices registered to the same account?