This functionality is easy to find in version 10 of Dynamics (GP). Ordinarily if you create multiple RTVs (Return to vendors) from a single RMA (Return material Authorisation) then the system will try and create one RTV for just one of the vendors.
However if you go to Tools > Setup > Project > service setup and go to the Returns button. On the RTV side you will find a consolidated check box. Un Check this box and the system will then allow multiple RTV's to separate Vendors.
In Version 9 however the check box is not there in the setup options. Instead it is on the window that appears when you create the RTV from the RMA. When you click process this box appears at the bottom of the screen and is very easily missed. Un check this to allow multiple RTVs to multiple Vendors.
It seems simple but that check box is easily missed (Rhonda at Microsoft pointed it out to me, thank you).
If you have any questions, please contact the firstname.lastname@example.org