Did you copied the complete Content of the two Folders? There is a global Setting "Options - Feeds - Remove Items older than". Do you remember the old Setting? Can you compare it to that on the new PC?
If you like to keep individual items for a longer time, you should use the "Flag" Feature. All items within a flagged Folder are kept forever, except you press the delete button there. All other items are bound to their individual item Age (at feed, at categories or globally controlled by the Setting mentioned above.
If you like to restore old items in the Cache, you really have to repeat the process copying files from the old Location. There is no garantee all your items are still in the downloadable Feeds...