Reinstalled Smartware - Backup Size is Smaller

I’m running a WD 1.0 TB My Passport external hard drive (not wireless). A few days ago I tried to do a back up and updated the software. The size of the backup was 302 GB and the list of files pending backup kept growing and growing, over 700 GB until I stopped it. Looking at the files there was a message about the specified path could not be found. WD support told me that if an update to the software is done this could be the cause, and I should uninstall Smartware, reboot, and do a fresh install. When I did, and opened the software and set a new backup, the backup size was now only 247 GB and it completed pretty quickly.

My question is, why the change in backup size from 302 GB to 247 GB? I’m not sure what the old version of Smartware I was running, the new one is 2.4.14 and it told me I would have to set up a new backup. Is this an expected result, and if not, what could be up? Thanks

It may be possible for the old version of the app to have an indexing error, or there was a category excluded from the current backup.