If I remember correctly the CAL contract had the 767-400 at the same pay as 777? The UAL contract had 757 & 767 grouped together at a higher rate that A320 and 727, but less than 777. The historical idea seemed to be pay the two together at a higher rate and more pilots will benefit than having 767 higher and 757 lower.
Also UAL was the kick-off customer in 1981/82 for the first 767. I think it was sold contractually as a size between narrow and wide body, 727/DC8 and DC10/747. We also had multiple pay rates for sizes based on GW; 3 727 rates, multiple DC8, DC10-10, -30, 747... it got a bit confusing, but in it all we never had a pay check screw-up.