Mail went missing from Mail Program

When I updated with a new email account in Mail my Inbox, Sent folders went missing. I was able to recover the emails from my Time Machine (10,000 messages) and they're in a DATA folder.

I was able to access my Library but when I try to add it to a folder I created in mail, the new folder doesn't recognize the emails. I labeled them the way all the other files are labeled in the other mailboxes.

Anyone know how I would add them again?

(For those that may ask how it went missing: I added a new Gmail account/email to the Mail program, which had a Verizon account/email.

I didn't do it correctly so I deleted that one and reentered a new Gmail email. Somehow it deleted the old info from the Verizon email account. I'd

kept a ton of sent messages there)