Thanks, Blanca. I’ll send more detailed answers to your email.
I’m unsure with which version I started the migration. I installed the App from the GSuite Marketplace. To start the migration, I went to the importing email account/Settings/Accounts and Import/Import mail and contacts, and clicked on “Import mail and contacts.”
It’s tens of thousands of emails involved, and only hundreds stamped with the wrong date. Or are they just the most recent to be imported? Difficult for me to sort out. After you’ve had a look, I may just cancel this import and with your guidance, start anew.