Thanks, EnTerr--
I did have a Private channel with the same name, for testing. I deleted it using the Manage Channels webpage (same as your link) after the new Version of our Public channel passed its tests and was published. The problem is that, although I deleted the Private channel using the website, it did not disappear from my device.
I have since verified with two subscribers that they see only the one channel, Public Version 1.20, the correct one. So evidently the issue affects only my device, and likely not our customers. I have now deleted the Private channel from my device using the * key. I still think there was a problem, but, as it likely did not affect our customers, it was not serious and has a simple workaround, so we can now consider the matter closed.
I have learned quite a bit about keeping tabs on Channel Versions. That Debug Mode that you showed me on my device will be very useful.
Thanks for your help, EnTerr.
--Gil