I can
definitely tell the difference in that first test!

That was quite a lot of UVA!
One of the easier nonvisual ways to tell the difference was in the leaf thickness. The leaves definitely thickened and stiffened up well before any senescence onset.
Now I do have some UVB fixtures with the fluorescent bulb like Migro has. I'm a bit leery of UVB. I just need to figure out how to schedule using them only a few minutes each hour. And I think I would use it only about a week to 10 days after flowering begins.
I don't know what to say, other than what manufacturer and what kind have you been using?