Hi Phil,
Up to know this looked like an <always 1> Tag to me.
Always and everywhere on all cams and lenses...
But know I have seen, that it is zero in all shots _without_ Lens!
beside that I see that Tags 0x1000 to 0x1104 now are all zero when you shoot without lens.
This is valid for a cold camera without lens switched on after a longer time being turned off.
When you quickly turn off camera, remove the lens, and immediately turn on and shoot without lens ... then closest Focus and current Focus can store (now invalid) data from last af-actions.
I think that this Tag 0x1200 not only indicates 'NoLens' ... it also indicates valid|invalid data for the whole 0x11nn segment.
-Klaus