Here's one of my notes, *RW5509415 (top) compared to *BA0641917 (bottom). My other note, *RW5498622 is similarly light. the two notes were aquired from different sources and are not washed as far as I can tell (no smell or ripples, althought the embossing isn't particularly heavy on either).
Maybe just a matter of ink mix at press time? All the other replacement 1974 $2.00's I've got fall in line with the *BA more or less.