As I posted earlier, I restored ~/Library/Application Support/AddressBook via Time Machine. Since it included the Metadata folder, I would have expected that that would solve the problem. As it turns out, the only contacts that I was missing were easily restored manually by re-typing the information.

I never actually lost my contacts, but I had to clone back from a clone that was about 2 weeks old. Fortunately, I had not changed much.

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365