Is an RMA record type the same as the PO?

Hello All,

I am creating some suite script on the item receipt transaction and have been trying to figure out how to determine when the item receipt was created based on a PO or from an RMA.  I take the internal id of the createdfrom transaction and then load the record casting it with the purchaseorder type. 

It was my assumption that when I try to load an RMA using the purchaseorder type it would flag an error but to my surprise it did not.  I then thought that even though it may have loaded correctly that when i did a getRecordType() function it would return the right type but it seems both the RMA and PO is giving me purchaseorder type.  I then further thought that I can grab the label using getValueText() but that function is unsupported in suitescript!  Does anyone have any idea if these findings are correct and what would be the best