Dynamic concatenation logically connects allocated data sets into a concatenated group. You can identify data sets to be concatenated only by their associated ddnames. These data sets must not be open; if they are, the request for dynamic concatenation fails.
The order in which you specify the ddnames is the order in which the system concatenates their associated data sets. The name associated with the concatenated group is the ddname that was specified first; the other ddnames are no longer associated with any data set.
If a ddname you specify is associated already with a concatenated group, that entire group is included in the new concatenation.
After the request for dynamic concatenation is satisfied, all members of the dynamically concatenated group are assigned the in-use attribute. The in-use attribute is described on In-use attribute.