Email Inbox did not transfer to new Macbook
I recently upgraded to a 2020 Macbook Pro from a 2017 Macbook Air. I am running OS Monterey 12.0.1. I was running OS Big Sur on the Macbook Air. I used Migration Assistant on 30 October 2021 to transfer files and data from the old to the new laptop. It all seemed to work perfectly. I waited about 4 days to see if I could find anything that was missed in the transfer, observed nothing, then reformatted/reset the old laptop so I could donate it.
Today (8 November 2021), I discovered almost all of the emails in my inbox that were dated prior to 1 November 2021 are missing. All other emails that were saved in my folders appear to have transferred.
My Time Machine has not worked correctly in a while so that is not an option.
I do have an iMac that has been running for 5+ years, with the same email accounts, on my home network.
Is there a way to recover the "lost" emails?
MacBook Pro 13″, macOS 12.0