Restored from back up and new back up size

Hi,

About 2 week ago I upgraded from an SE to a 14 Pro. When I set up my new 14 Pro I restored the phone using my SE backup. This back up was about 12 GB. Now what I can't seem to figure out is why the new backup size on my 14 Pro is only about 700 MB. Correct me if I am wrong but shouldn't my new back up size be about 12.7 GB? I thought the new back up would include all the previous (SE) data and the new (14 Pro) data.

I am aware you can not consolidate iCloud backups but in the event that my I need to set up a new phone or transfer to another device, which back up should I choose to restore from? If it is the 12 GB SE back up, what happens to all the new data stored on the 700 MB 14 Pro back up?

I have been trying to figure this out and any help would be appreciated. I am just worried about losing data!

Thanks!