I ended up buying a couple more of these over the past ~6 months or so when they popped up cheap, just now getting around to looking at them. Listed below is the SN vs date (newest component date I could find) vs front panel color vs today's 10v reading:
SN = 4150027, 1986, white faced, 9.9998328 (9.9998030, read by our friend @CalMachine in Feb of 2017, ENI Cal Labs, 25C)
SN = 3075014, 1982, white faced, 9.9999200 (New NiCad date of 2004 sticker inside)
SN = 450007, 1976. black faced, 9.9998050
SN = 84405, 1974, black faced, 9.9999182 (731A)
All 4 had no Cal stickers, so who knows how long it's been for any of them. Read via in Cal 3458A, 200NPLC, mental average of LSD bobble, 24C lab.