At startup for a "clone" CV joining DSGROUP=TECH the messages were:
DC202001 V51 Starting WARMSTART
DC215999 V51 IXCJOIN RC=00000000 Reason=00000000 Name=TECH
DC391504 V51 #XCFGRP FUNCTION=SETUS failed with R15=00000008 R0=00000008
USER COMPLETION CODE=3962
IDMS - All Supported Releases
The attempt to join the DSGROUP failed because the member name specified in SYSIDMS DCNAME parm was the same as the primary CV which had already joined the DSGROUP using that member name.
SYSTEM OPERATIONS GUIDE, Chapter CA IDMS in a Sysplex Environment, section "Specifying Group Membership" , USAGE section:
Specifying a group name
All CA IDMS systems that specify the same group name are members of the same data sharing group and are therefore capable of sharing update access to data as well as exploiting other features associated with data sharing groups.
** Specifying a member name
**
** Member names must be unique within a data sharing group. Member names should also be unique across your environment since the member name becomes the system (node) name.