I will look into Super Duper, as TM and CCC are unable to incrementally "update" the 2nd Mac without fully erasing and migrating a TM Archive, or erasing and cloning a CCC backup.
The goal is to do all updates on Mac-1 and then update (incrementally over time) a "clone MacHD" on Mac-2.
I have TM on Mac-1 updating 2 drives, an attached TM USB drive, and, it also logs in and updates a 2nd TM drive over the LAN attached to Mac-2, but only if it stays permanently attached.
If Mac-2 is not running during a Mac-1 TM backup, it can no longer recognize the Mac-2 TM drive logging in over the Lan, or even if it is loaded manually onto the Mac-1 desktop. The only option is to wipe the Mac-2 TM drive and start a new Archive (4+ hours).
After using a USB boot drive to fresh-install 10.12 on Mac-2 and migrating from the latest Mac-1 TM Archive (2+ hours),
TM on the new Mac-2 MacHD is unable to recognize the TM backup that just created it,
therefore, in the future, it cannot go "back in time" on that TM drive, to an already updated Mac-1 TM Archive, so "updating" Mac-2 with future TM updates from Mac-1 are not possible.
CarbonCopy Cloner, same problem - CCC makes a clone of the Mac-1 MacHD, but there is no way to use that clone-file to make incremental "updates" of the Mac-2 MacHD, unless it's a total erase and clone.
Why is a newly created MacHD TM app, just created by migration from a TM Archive attached to the same Mac, why is that TM app incapable of recognizing the TM Archive that just created it?