the LAD patch for the TAF film is actually used to calibrate a telecine to be used as a starting point for film reproduction as a reference for Dmax/Dmin and middle grey (LAD) as well as to setup the blacks, whites, grays and saturation levels.
The LAD patch itself should correlate to 39 IRE (Composite) and 45 IRE for (Component).
What you might be referring to is that a grey card, according to the Kodak TAF White Paper, should correspond to 45 IRE ,which serves as a starting point for colorists to set up their grades and take the guess work out of how the sceen was/is suppose to look, ie white is 80 IRE, Black is 20, and Grey is 45 IRE.
And of course, as I'm sure you know, all of these IRE's correspond directly to a mV value for a CRT monitor in order to reproduce color and luminance in a repeatable and precise manner.
Hope this helps. All this info can be found here: Link
Another invaluable reference: Quantel Digital Fact Book