Sorry for my late reply and I was just back from vocation. Thanks for your cooperation again! And now I totally get you.
I believe this is what you need:
=IF(AND([Will training be required for this change]="Yes",OR([Has BIA/HLIA been scheduled]="No",[Has BIA/HLIA been scheduled]="",[Has BIA/HLIA been scheduled]="Not yet scheduled"),[Is Comms required]="Yes"),"Training,Comms",IF(AND([Will training be required for this change]="Yes",[Has BIA/HLIA been scheduled]="Yes",[Is Comms required]="Yes"),"Training,BIA,Comms",IF(AND(OR([Will training be required for this change]="No",[Will training be required for this change]=""),[Has BIA/HLIA been scheduled]="Yes",[Is Comms required]="Yes"),"BIA,Comms",IF(AND(OR([Will training be required for this change]="No",[Will training be required for this change]=""),OR([Has BIA/HLIA been scheduled]="No",[Has BIA/HLIA been scheduled]="",[Has BIA/HLIA been scheduled]="Not yet scheduled"),[Is Comms required]="Yes"),"Comms",IF(AND([Will training be required for this change]="Yes",[Has BIA/HLIA been scheduled]="Yes",OR([Is Comms required]="",[Is Comms required]="No")),"Training,BIA",IF(AND([Will training be required for this change]="Yes",OR([Has BIA/HLIA been scheduled]="No",[Has BIA/HLIA been scheduled]="",[Has BIA/HLIA been scheduled]="Not yet scheduled"),OR([Is Comms required]="",[Is Comms required]="No")),"Training",IF(AND(OR([Will training be required for this change]="No",[Will training be required for this change]=""),[Has BIA/HLIA been scheduled]="Yes",OR([Is Comms required]="",[Is Comms required]="No")),"BIA","No Readiness activities")))))))