Hello,
my ADR1000 #3, currently 6.668563V, is now running for 1 year.
Its oven is set to 51.4°C, and it has got no initial conditioning / heat treatment.
In the diagram, you see its absolute drift, i.e. relative to the median of my group of 8 references.

Over the years, I determined the average drift of this reference group so I'm able to make absolute drift measurements to < 0.5ppm uncertainty. This is confirmed by the recent 'baseline' measurement of -0.17ppm in June 22, which is derived from the ring comparison organized by branadic, where two members had calibrated uncertainties of < 0.5ppm each, and I, No. 7, was measuring the travelling LM399 right in the middle between both:
https://www.eevblog.com/forum/metrology/eu-calclub/msg4385281/#msg4385281Therefore, my ADR1000 shows -4ppm/6months when constantly powered between November 2021 and May 2022.
I didn't power it in October 2021, and in June 2022, to check for hysteresis effects.
This turned out to be +2.8ppm in Oct. 21, and up to +2.2ppm in June 22.
On latter tests, I switched it on 12h prior to taking measurements, but in the end did not investigate on how long it takes to reach the previous "warm" value.
I add a comparative drift measurement on two pre-conditioned LTZ1000A, which show -1ppm/6mo. at most, and seem now to stabilize to much smaller drift rates for the last 7 months.

The FLUKE 7000 shows -1.4ppm/year in 2021, which is quite mediocre. So it is used as a stable 10V transfer standard further on, as I changed its output value twice for my experiments on the 752A and 720A dividers.
So my conclusion is, that the ADR1000 at current is not suitable for serving as a volt-nuts reference like the LTZ1000, due to its high annual drift and big hysteresis. A working burn-in procedure would be required. In the datasheet there's a hint that after 3000h @ 75°C the drift will be reduced to 0.5ppm/Yr., but I don't know if anybody has tested this.
Frank