When initially testing these, there was just a single zone in the catalog

When adding the real zones to be carried by the servers a shell one-liner script was used to update the catalog zone, but by mistake it neglected to terminate the PTR targets in a period - which led to the zones all accidentally picking up the $ORIGIN catalog.db and appending it to the zone names.

The next steps fixed the catalog zone, updated the serial number, and reloaded it.   The slaves transferred the new catalog zone but did not update the zone list as a result of the changes.

Is this perhaps because a domain name hashes the same regardless of whether it is period-terminated, and that BIND may be keying its change notification on the addition/removal of owner names in the catalog,
rather than looking at the entire record.

It took an 'rndc reconfig' to get BIND to notice the changes to the catalog.