How does MRP Demands work with Safety Stock?
Setup an Inventory Part #101-0002525 with Safety Stock of 500 for Mfgr - KOA (if Safety Stock is listed in Genr system will use qty from any of the AVLs to full fill the Safety Stock).   Dale having a Qty on Hand of 100.  (Note:  Safety stock is calculated at the AVL level not part # level)
 

MRP Demands - Displaying Required Qty of 500 for Safety Stock and 450 for a WO release - MRP Action List is saying to Release PO's for qty of 500 and 350  

Projected Inventory is displaying that there is available inventory of 100.  To fulfill the requirements user needs to  release a PO for 500 and a PO for 350 (using the available qty to full fill the WO demand.   

 
Drill down to Create POs and here is where system will tell you which mfgr to release POs for to full fill the demands.