Joined: 06 Jun 2008 Posts: 8165 Location: East Dubuque, Illinois, USA
The CA-11 user manual says
All simple (non-GDG) data sets whose first DD reference is with DISP=NEW are uncataloged and also are scratched if on disk. This action prevents NOT CATLGD 2 situations. This catalog and data set maintenance is not performed on data sets which are exempted from it by the CA-11 user exits, U11RDSEX or U11UCSEX, or the CA-11 Volume Include/Exclude List.
It sounds like DISP=MOD is not treated the same way.