The theory on Monthly Meeting categories, as we received it, was to multiply categories with each change. This is, however proving to be unwieldy (more so with the numerous splits and mergers than with name changes, thought).
In this case though, since it was the precursor meeting and it did not become Plains until as recently as 1966, we could make a good case for a West Glendale category.
I don't know. The concept of having separate categories for the same meeting which happened to change its name did not sit particularly well with project members, I personally think it's too complicated, but it's still the official guideline...