My backup paranoia vindicated.
A Mac User Group member has finally updated her iMac from OS X Snow Leopard (10.6.8) to another with El Capitan (10.11.6). She wants to transfer her contacts from her old Time Machine drive to the new iMac. But because of past problems caused by Migration Assistant she will not use that process.
My (paranoid) process for the last 8 years has been to make a weekly archive (.abbu format) of my contacts list & store it in Dropbox. This is in addition to multiple Time Machine & Clone backups. Plus, I use iCloud across all my devices and back up the OS whenever a new version arrives.
Ergo, I always have a way to rebuild the contacts list should it be needed.
But Kathy's sole source of backup is a Snow Leopard Time Machine backup. I have told her of the process recommended by The Mac Observer to restore such info from her old backup.