The voltage reference has been baking for 1000 hours, give or take a few. The power went down for a few hours during the test, but I don't think it matters much. Here's the results, using the same conditions as when the test began:

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2019-07-01 1000hrs at temp

Set Point: = 0.627049

Value         Range    Aging Drift
100.0065    100mV   9 ppm ±2ppm
1.000023   1V           18 ppm ±2ppm
2.49993     10V         16 ppm ±8ppm
4.99922     10V         18 ppm ±4ppm
10.00007    10V          1 ppm ±2ppm

I find it a bit suspicious that all of the voltages drifted upward over time. That would indicate a drift in the measurement tool more than the references. I put tolerances on the aging terms just to account for the uncertainty of the last digit over two measurements. 

I don't really see a need to open the box to perform any trimming.