Hi, I finally figured out what was confusing me so about this. In case other people are going around the same circle I was:
Creating a galley without the Public Galley Identifier option turned on arranges the "Edit a Layout Galley" section of the "Galley" page so that a message is directly below the field it relates to: the next item after the "Label*" field is a note that "The galley label is used to identify the item's file format (e.g. HTML, PDF, etc.)." Good: the thing and the explanation of the thing are together.
Turning on the Public Galley Identifier option changes what is on the page, placing the "Public Galley Identifier" field directly between "Label*" and its explanatory note. So, now there is a field that should contain something like "HTML", a blank field, and then a note below the blank field suggesting something about "HTML". Hm. I eventually slowed down enough to figure out that the explanation pertained to the "Label*" field and not to the nearer "Public Galley Identifier" field, so I am rolling again: "HTML" is a Label, possibly for many things; something else, something unique per article, is a Public Galley Identifier. A more user-friendly design, though, would always keep a field and its explanation together, no matter what other fields come and go on the page as options are enabled and disabled.
Thanks for OJS. I am having fun with it.