There are several reasons for differences between the tables.There can be differences in the yield strength of the material of which the calculations are made.  The Differences may be due to the method of calculation for which the value is obtained.  For example, flexural resistance of a composite slab can be determined using the “Prequalified Section”, the “Shear Bond” or the “Ultimate Strength” methods or performance testing.  Some manufacturer’s tables include LRFD and others include ASD or LSD methodology, which would have different values.  Differences can also be due to slight variation in profile shape between common profiles.