OK, I think I may be beginning to understand why I'm having so much trouble trying to convert drives E/ thru G/ to being Logical drives.
MBR drives, D/: and H/: can have both primary and logical partitions.
C/:, E/:, F/:, and G/: are GPT drives.
Their 1st partition must be primary.
C/: requires primary because of the OS.
I set D/: as primary because of plans to install applications there rather than on C/:.
E/:, F/:, and G/: have a single partition and are GPT.
H/: is MBR allowing it to have its single partition to be logical.
Don't know how clear that is to everyone else, but I understand it.
I may not like it.
But, I now understand that's how the world works.