Explanation on what ACSMFEXT (in ACFSMF macro) is and why its offset is extension = 0
Release : 16.0
Component : CA ACF2 for z/OS
ACFSMF D uses ACSMFEXT for X.500, MLS, TAMz, IDID data, and Active library lists. Not all SMF records use the extension field. Therefore, in some circumstances a zero is acceptable.