Bear in mind that I am just making observations and don't want to come off like some kind of expert. I don't know a lot about AZO but what I know for a fact is that most people are using light sources for exposure that put out very little or no UV radiation. And if you look at the spectral sensitity curve for AZO you will see that it has quite a bit of sensitity in the visible range at about 400 nm in the violet, and still quite a bit at 450nm in the blue.

Yesterday someone contacted me in response to a message I left on the BTZS web site regarding BTZS testing of stained negatives. He had tried this with AZO using the blue channel of his densitometer and the resullts did not match the times he knew to be correct from practical testing for N development. I can see that this would be a problem wiht AZO since the exposing light used by most people does not match the maximum spectral sensitivity of the paper itself.