At least for the standard x10, x100, and x1000 values I think they are all the same. Some of the later values which were introduced might have varied between manufacturers.
As far as I know, the original standard came from Barry Gilbert when he designed the readout for the Tektronix 7000 series where the probe readout resistance directly alters the 1 of 10 encoded current into the analog readout generator. It is possible to go though his design to calculate what the resistor values should be.