"The GAF is a 100-point tool rating overall psychological, social and occupational functioning of people over 18 years of age and older. It excludes physical and environmental impairment."

-as that states, the GAF is not what is going on a particular day. It is almost a snap-shot of how you are able to be productive in the world, care for yourself, etc.

The word global indicates "the entirety of the world" but in this case refers to an individual in the world, so it can describe, very generally, how well a person can function in all arenas.

Also: even if a scale or assessment tool is no longer in use, results from such tools are still valid and relevant now, since they were determined using a valid scale/tool.