There is a chance the edit still lives – if you have access to the originating machine or a backup, there would have been an ‘Autosave Vault’ folder in the Final Cut Pro Documents folder…
I’d run Disk Utility on the external, see if there are errors. Given the age of the project (and your setup), I’m assuming the external is formatted HFS+ (Journaled) – if that’s the case, I’d also run DiskWarrior on it.
There is no way to switch video angles and also keep a specific angle in the same multicam clip hot at all times. Just overlay the scoreboard clip once you’ve done your multicam cut, and scale/position as desired.
That’s odd. Could be that only one of the clips took the change in the inspector… I’d select the clips one at a time in the browser and make sure that actually got set. You’ll need the General or Extended panels in Inspector to see the ‘Camera Angle’ entry field – ‘Camera Name’ may not be sufficient.
Aside from that, what are the rogue angles named in the multicam clip?