What I would suggest is making a third table, call it tblDisc or something. This table would have the following fields:

DiscID
MovieID
LoanStatus

This way you can keep track of all the movies on each disc and still have unique MovieIDs and titles. Depending on the database you're using, you can make MovieID a foriegn key. This way if LoanStatus of the disc changes you will have a way to update the LoanStatus...