Thank you, Chris. That is all good info.
But,
That is the option I chose from the menu offered by the ISO installer, so I expected an install using GPT, not MBR, even if the disk may have been previously MBR, which I can’t remember (old age being what it is 
).
What I observed is what I would consider some logic by the installer deciding that MBR was the way to go … and I don’t understand why that would be the case for a physical hard drive of very standard make:
ID-1: /dev/sda vendor: Western Digital model: WD5000AAKS-00V1A0
size: 465.76 GiB speed: 1.5 Gb/s tech: N/A serial: WD-WMAWF0060756
fw-rev: 1D05 scheme: MBR
Since I don’t have much invested in that installation, I am planning to redo that, but with manual control, using Gparted from the Live ISO, before performing the install.
I just don’t understand why I have to redo the install to get the GPT on that drive. I’m just saying that I think maybe there must be some logic (which needs to be reviewed) that may have “preserved” the MBR when, for a “reformat and overwrite” directive, it should have rebuilt the Partition Table using GPT.