More recent releases of the ALF sitcom season 4 DVD set (US releases) seem to be missing two episodes. If you have a US release (UPC #0-31398-20121-0), your season 4/disc 3 should contain the following episodes:

13. It's My Party
14. Make 'Em Laugh
15. Love On The Rocks
16. True Colors
17. Gimme That Old Time Religion
18. Future's So Bright, I Gotta Wear Shades

The faulty discs have the episodes "It's My Party" and "Make 'Em Laugh" missing from the DVD set, and the episodes "I Gotta Be Me" and "When I'm Sixty-Four" are repeated on both discs 3 and 4. Below is the message issued by Lionsgate Entertainment on this subject.

Dear Consumer,

Thank you for contacting the Lionsgate Customer Service Department.
Please send your disc (disc only is fine) to the below address. Once received we can send you your replacement.
(US address only)

Thank you!

Address:
Lionsgate Entertainment
Attn: Customer Service/Operations
2700 Colorado Ave
3rd Floor
Santa Monica, CA 90404

Additional information on this will continue to be available at the ALF TV Fan Forum.