iCloud sync losing contacts

My MacBook Contacts were previously not syncing with my iCloud account, which meant that they were out of sync with my iPad (which WAS syncing to iCloud). To rectify this, I enabled iCloud syncing for the contacts on my MacBook. It asked me if I wanted to merge the Contact list on my MacBook with those in my iCloud account, which is exactly what I wanted.

The merge was executed, and the contact lists on my MacBook and iPad are now identical, BUT many of the contacts from the MacBook were lost in the process. The contacts in question were all members of a folder that I had created under the iCloud account in the Contacts app. While some of the entries in this folder were synced correctly, most were not. They now no longer exist, either on the MacBook or iCloud.

Typically, the contacts in this folder would have been created from emails - i.e. by selecting an email sender and choosing the "Add to Contacts" option.

For some reason my Time Machine backups are not showing any entries for Contacts (my last backup was taken only yesterday).

Any idea why these contacts would have disappeared during the iCloud merge/sync process, and how I might be able to recover them?