Mail App "All Inboxes" view treatment of duplicates from multiple instances of same email account

iPhone Mail App. (12pro. 18.6.2). About a month ago one of my AOL email accounts stopped syncing and I'd get a "password incorrect" pop-up every time I go into the mail app. I tried multiple times over a couple days to re-enter the password, but it never worked. Checked the settings, nothing seemed obvious, nothing had been changed, and my other AOL emails were continued to sync without issue. I finally gave up and decided to delete and re-add the email. I thought it best to first re-add the email before deleting the existing one so that if there were a larger sync tech issue with AOL, at least my older emails were still on my phone.

It worked, and the new "install" of that account started syncing and all the emails eventually synced up, so I now have two installs of the same email account on my mail app, with only the newer version syncing new emails, but all the older emails are on both if I open each specific email view. So, I assumed the "All Inboxes" view, which is what I normally have open, would show duplicates once the older emails synced up on the new install, but it doesn't, which seems odd since they are two separate mail account "installs". I'm not worried about permanently deleting emails, but I do care about what I can view on my phone so before deleting the older install I would like to understand why, in my particular scenario, I'm not seeing duplicates in the "All Inboxes" view, because it seems like I should. I can't find any info on this and am not willing to test it by adding a 3rd "install" to see if two active syncing same email accounts would produce duplicates in the "All Inboxes" view, so I'm hoping someone has had a similar situation and can shed some light on it.