Thanks again. Over two days we received two Series 10 watches, one from Apple; one from Amazon (might have bought both from Amazon for the 5% cash back using the Amazon/Chase Prime card, but Amazon didn't have color my wife wanted, so we paid a little more buying direct from Apple.com).
One fairly remarkable thing. Both watches and Apple Care + were bought on my account at Amazon and at Apple, respectively. Bought at Apple on my account for the Veteran discount. Nonetheless, by the time the watches were set up, they both show up on the correct Apple accounts, including the Apple Care +. I had frankly expected to have to call and get whose watch was whose, but didn't have to.
One more thing about upgrading from old to new watch. If you have two watches and iPhones, keep the watch and iPhone you're NOT using out of the room where you're working on the backup/unpair/pair process. We had a false start when my iPhone tried to pair with my wife's new watch (or my wife's iPhone tried to pair with my watch...I'm not sure. Anyway we started over with only the old watch 5 and new watch 10 plus the related iPhone in the room!