It's been more than 1 year since I purchased the Keysight 34461A DMM. It is officially out of calibration now. Time to do a quick measurement. I powered up the voltage calibration box (the Digikey box) and the DMM for six hours prior to taking a measurement. Here's the results:

DIgikey Box:

Ambient Temp: 68°F(20C)

DMM settings: 100PLC, Auto Input Z (High Z)

Reading (not averaged)    Scale

99.9994mV (nulled)          100mV

1.000011V                          1V

2.49976V                          10V

4.99940V                          10V

10.00003V                         10V

These are not very far off from the six month readings.

AliExpress Box:

(same settings and ambient temp as above, soak time 4 hours)

Reading                                            Scale

100.00181mV (avg/20 samples)        100mV Nulled

1.000035V (avg/20 samples)           1V

2.50014V                                           10V

10.000114V (avg/20 samples)              10V

Current Reference(all readings 100plc, averaged with 20 samples):

Reading             Scale

10.001474mA     10mA

0.999977mA     1mA

99.99313µA       100µA

General Conclusions:

All of the voltage references seem to be very stable now. No significant difference between the USA components and the Chinese components. The current readings are drifting a bit, but the specs of the 34461A are quite a bit looser for current than voltage. The only way to tell for sure is to compare readings to a calibrated DMM with >6.5digit capability. That's not happening anytime soon.