UPDATE.
As of today (4/4/19). the old, returned-as-defective Note 9 is no longer listed on "Your devices." Why is took so long to go away, I have no idea. I can't say if the Pie update had anything to do with it.
The big tomato-red option banner to "remove device" is still not there. So this 'miraculous correction' happened on the heavenly, Google-Verizon-Samsung-Godhead side, and not in any way through the will of one of its mere creatures.
However, this divine intervention was incomplete: two instances of the same old, no-longer-used Samsung 310 tablet still appear, and both instances say that it was last used on March 10, 2019 (when I replaced and tested the motherboard).
Google is not what it's supposed (and claims) to be. However slight the risk, it's still a security hole if an old device can not be removed from an account by the registered and logged-in customer.