Can I check the you used the copy and rename method (or shift-start-iTunes) to access the older library files? Double-clicking .itl files opens iTunes, but not necessarily the file clicked on.
Did you check for .tmp files in the iTunes folder? One of those may have been your most recent complete library. Otherwise without a proper backup the best you can do is use your most recent file from the Previous iTunes Libraries folder and use the suggestions in the tip to bring it up to date with the contents of the media folder.
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