Pretty much crickets in terms of interest in this, but in case this helps anyone at some point.
The Ethernet transfer was finally completed. During the process, these things occurred:
1. a situation of no increase in the number of events transferred for some 16 hours, until:
2. a complete hang of the H3, presumably caused by someone going into the Netflix app. Restarting the H3 from the menus of a still-connected 4K Joey resolved that.
3. a restart of transfers by breaking them up into smaller chunks, say, 40 events or so, resulting in the need to continue to restore from trash on the sending H3 with:
4. some progress, until hours after accepting the option to go Watch TV, a completely unexpected reboot of the H3, causing me to:
5. copy even more events to the external drive before resuming the Ethernet "transfer"
6. eventually resulting in a Complete message including the helpful "116 of 38 events transferred".
It makes one shake one's head somewhat ruefully.
It makes one ask, I wonder if a USB-to-USB H3-toH3 transfer would work. But mostly, if makes one say, next time, transfer everything to an external drive, adding drives if necessary, instead of wasting time with the half-baked Ethernet method.
I think the transfer software was designed to cause the user to just give up and decide that that crap on there wasn't needed anyway.
I still have the question posed earlier about whether I need to clone my new H3's drive or simply have a bare unformatted ST2000VM003 on hand if I have a hard drive failure.