As shipped, MSTJCL00 contains an IEFPDSI DD statement that points to only one procedure library (SYS1.PROCLIB) used by the master subsystem. You can place individual jobs in any other procedure libraries pointed to by the IEFPDSI DD statement.
As an alternative to placing individual jobs in any of the other procedure libraries pointed to by the IEFJOBS DD statement, you can instead put jobs in the members of SYS1.PROCLIB or other data sets in the IEFPDSI concatenation. In this case, you must make sure that there is not another member of the same name in one of the data sets in the concatenation ahead of the data set containing the member with the source JCL.