re pc reset followed by removed app email program and replacement new email program

After a pc reset in Windows 10 my email program Windows Live Mail 2012 could not be reinstalled from list of removed apps as support for Windows Live Mail ended in January 2017 but I still kept using the version I had already installed.  A tech person helped me to install Thunderbird email program.  I had not made a backup file for my Windows Live Mail 2012 but the tech help was still able to recover a lot of email from 2010 to 2016 and covering new incoming mail from November 1st 2017 in Thunderbird.  My question is why did he recover most mail but lose the period from May 2016 to November 2017?  I feel that there must be a way to restore this missing mail to import to Thunderbird ie. before November 1st 2017.  I don't believe it is lost but just stuck somewhere in my computer and I would like to know how it might be restored realizing that the old program cannot be reinstalled.  I would appreciate any help you could offer on this.  Thank you very much.