Slim,
That's because they switched to piezo equipment within the past few years, so started testing every new product (whether bullets or powder) in PSI.
They didn't run nearly as many powders with the 85 TSX as they have with older bullets, particularly in the slower burn-rate range where IMR4451 stands out. Check out their .243 data for the 90-grain Speer bullet: the velocities for 4451 lag behind such "new" powders as H4831 and H414/W760.
Have you ever actually done any work with pressure-testing equipment, whether strain gauge or piezo-electronic?
