iPhone – How to Prevent Multiple Device Backups in iTunes

I was snooping around iTunes recently and navigated to the Devices Preferences tab and found 3 backups in the Devices backups list. I never realized when I would get new devices through the years and would do the Restore from Backup thing from a local backup that I was apparently creating a new backup during that operation. I always assumed I was merging backups into a new phone but now that I look it appears that I must have been taking an existing backup, loading it onto the new device, and splitting off a new backup offshoot for that new device while the old backups then sat around waiting for those old devices to connect or something.

I can even see the three distinct folders dedicated to these three backups on the file system. The current one interestingly enough takes a different GUID form than the older two which seem related to each other in that there's a suffix used to differentiate the two.

Is this understanding expressed above accurate? Is this how the multi device backups work and are generated? Is it even possible to restore a new device from an old backup that belonged to a different device? Is the checkbox option Prevent iPods, iPhones, and iPads from syncing automatically responsible for this split backup behavior? Maybe it's just a fallacious premise to think that multiple devices could even share the same backup and merge their data all together in one big enchilada on disk.

(My memory could be off on this one since I didn't monitor the operation closely when I setup my new phone last Christmas. It could be there's old files and folders that didn't wind up in my new device which would suggest I did not restore from an old backup file but from other material found on my PC and my iCloud account. I did find my contacts and probably my iCloud photo instances present so assumed everything else restored from those old backups but now I'm not so sure.)