Quoting the calibration uncertainties at 99% level sounds weird when most of the stuff is quoted at K=2 95% level but I'm too lazy to check what ISO 17025 has to say about it.
(stability specifications are often quoted at some other level)
I thought (without any evidence) Fluke sticks to their 99% levels. The old instruments (5440B, 5450A..) are only specified at 99%. Only the "newer" ones has additional 95% specs to be comparable with other equipment.
Both Keysight and Fluke in US have their own Josephson standards, apparently Fluke Deutschland also has one and guessing from uncertainties I'd say that Fluke Norwich also have their own.
The next calibration of our 8508A will take place in germany, I think.
It's confusing, but maybe this will help clear it up.
Fluke uses 99% CL in their manufacturing quality control and so the guaranteed specifications are presented at the 99% CL (for a great explanation of this, see
http://download.flukecal.com/pub/literature/msc04.pdf).
The 95% specifications are listed due to contract obligations from a specific organization that requested published 95% specifications as a requirement in order to buy the calibrators.
Don't use the 95% specifications unless your supporting lab verifies the calibrator to the 95% specifications. Why? Because if you have a unit that is out of tolerance and needs repair, you may send it to Fluke, who, by verifying it at 99% specs, may not see a problem.
The confusing part is that labs use measurements with uncertainties presented at 95% to compare to Fluke's 99% test limits to determine pass/fail. It's confusing until you are convinced of the fact that your measurement uncertainty CL has nothing to do with the CL of the specifications you are comparing against.
If Fluke's 95% published specs were proportional to the 99% by a constant (they are not), you *could* use the specifications @ 95% even when tested at 99%. But until someone from Fluke clears this up, I"d avoid the 95% listing altogether.