What is an acceptable amount of blow by?

What measurements for crank case pressure are considered "in spec" for a newly rebuilt X15 by Cummins when measured in inches of water with a manometer? Does the tolerance vary for a new and old engine? I was getting high crank case pressure codes when my truck would do a regen but when pulling a load at full throttle no codes came up. Engine was recently rebuilt 30k kms ago. One shop told me my crank case pressure readings were nearing the upper limit of tolerance when under load but now the shop who did my rebuild is telling me that they opened a case with Cummins and everything is "within spec" for a newly rebuilt engine after they replaced my non serviceable crank case filter.