Restoring address book with Time Machine

I have had some issues with my address book, which I won't bore you with. Basically I needed to restore my address book from a previous day when I knew it would be ok. I deleted my current address entries and then went to time machine for a restore. It worked really great, except, it did not restore the groups that existed previously. The groups are actually shown on the back up file, so I am at a loss why it did not restore groups as well as the contacts. Any advice would be really gratefully received. I am a recent convert and am very satisfied with Mac and so happy go leave PC behind.

Many thanks

Michael