Schedule Line Category and Availability checks

Hi Folks,

A generic question.

Wanted to know, how would availability check results influenced if only Item category and MRP type are maintained and not the scheduled line categories.

Was trying to figure a strange Availability check behavior of non-confirmation for one item category and confirmation for another- item x location being same. The ATP checks settings are maintained and called from GATP. (not R/3 and R/3 customization is not imported too).

Regards