The two sessions can easily be made to invoke different versions of IOF. Different LOGON procedures can be used, for example. See question T02 for another technique for running specific versions of IOF.

The IOF8x execs described in question T02 can not be used to initiate different versions on the same TSO session. These execs "SELECT PGM(IOFSPF)". Once the IOFSPF load module is loaded into an address space, a second call for the same load module will use the existing copy, resulting in the same version of IOF being initiated. In addition, the concatenation technique used for the SYSPROC and SYSHELP files causes both split sessions to use the same concatenation.