Date Added Value in Itunes

I had to chnge the location of my itunes library due to space constraints. All of the music seems to have made the trip. However, all of my music now has the date of the move as the date added. This is a problem because I have quite a few smart playlists that are essentially the songs added during any particular year or period of time. Any suggestions on how to get my original date added back? I'm really more interested in the date the song was purchased in the Store. Thanks for all the help.