Yes, there is an InstanceBeginEditable named "head" in the appropriate place in the template (and a corresponding closing tag). When I evaluate template syntax it's fine.
It is, alas, a little more complicated than that. I am working with a site that was set up (not by me) with nested templates. (We will be moving out of this system within the next year I hope.)
The "basic page" template is the parent of the "pmg page" template, which is the parent of the child pages that don't show an editable region named "head".
The basic-page template has a Template Editable name="head" region, which correctly translates into the child template as an Instance Editable region.
The problem is that there are several Instance Editable regions in the child template that DO successfully propagate to all the (grand)child pages. There is only one that does not, and it's the one named "head" that consistently fails to propagate.
I could, if I had to, create a Template Editable name="head" region in the child template, and maybe that's the solution. But further insights if any would be useful.