RecentX 4 does not upgrade the data from RecentX 3. So you may not find some recent files that you had accessed using RecentX 3 on Windows pc.
However, since RecentX indexes all files on your hard drive, you should be able to find any file in RecentX . But make sure you choose "All" option and not "Recent" option in Files list and Folders list.
Once you choose "Reindex" option in RecentX , you would need to restart. It takes some time for RecentX to index all the files initially. If you just leave your computer idle, within 15 minutes, it should index all the files & folders.
Don't use Reindex several times. Do it once, and let computer index during idle time.