No, the yellowing (in prints made by Kodak) is not due to insufficient washing. The yellowing is due to the nature of the fibre base to absorb the processing chemicals and become stained by them, regardless of how much one washes. I have never seen a fibre based color print that had as nice a white border as modern RC color papers. The bleach used in color print processing is quite staining, in my opinion. something we don't find in b/w printing.
So are you saying that they come out of the lab yellow rather than yellowing over time?