Thunderbird and Gmail problem

[JD]

Had a disk corruption and lost inbox messages from Dec 17, 2015 to June 
15, 2016
So, I followed the tips online:
1. Exit TB
2. Login to gmail account via browser
3. Click on cogwheel on upper left of browser screen
4. Select Settings
5. Click on  Forwarding and POP/IMAP
6. Click on Enable POP for all mail (even mail that's already been 
downloaded
7. Scroll down and click on Save Changes.

Restarted TB, logged in and I received ALL messages.
However none of them were for the date ranges that I lost.
So I used a plugin to delete duplicates.

Yet, on the browser, I can see those messages for the date range that I 
want.

How can I force them to be downloaded again?