I asked my Dad where he read the ap note on the LTZ1000, and he didn't remember. He only mentioned it in passing over the telephone when I was working on a LTZ1000 reference. But I did mock up a LTZ1000 reference and push on the IC a bit, and the voltage output changes.
Now, for Lars graphs; Good, solid work. I'm happy to have the info. If the unit was designed to operate at over 50% RH, I'd have a problem. But the standard is designed to be operated in a controlled environment not to exceed 50% RH, and with a temp between 17-26C.
I haven't done any testing at RH above 50%, because I work in a standards lab with a controlled environment (RH 30-40%). I wasn't aware there was a market for high-humidity, low-cost standards. But, in any event, the unit is not designed to operate above 50% RH or above 26C.