I agree that option 1 is possible. I also agree that option 2 seems highly unlikely.
But there is a 3rd option: perhaps your multimeters are ~3% off?
As the Fluke 73 has a preset adjustment, that is very plausible indeed - we have 10 or so Fluke 75s in the Funds lab at work, and when I calibrated them all a couple of years back, some were out by several percent. If you obtained it second-hand, who knows what the history is? This is what started this thread, after all.
So from everything that has been written so far, I haven't
quite been able to rule out option 3. I can't say that it
is the explanation - I'm just saying that I haven't yet seen enough evidence to discount it.
But I've offered a couple of hints and suggestions that could convince me. The checking of the LM385 (see post #73) in your Fluke 73 is the easiest/quickest option, but taking up my offer of a free LM4040 that has been measured before dispatch would also be good. You'd then have a "transfer standard" that you could use to calibrate your meters...
Re. your UK supplier - it sounds like he/she is a "drop shipper". Very common, and I've been caught out by that in the past. By "caught out", I mean that I paid a couple of pounds more to buy from a UK supplier in exchange for a faster delivery time, only to find that the thing came from China or Hong Kong. Live and learn
