[Edi]

For predesigned start locations that always appear in those places but place a random nation there, use #star <province number>. Just make sure the province is not labeled nostart in the map editor. #start slots will always be filled first and any leftover nations will start from random eligible spots (i.e. some province that is not nostart). IF there are more #start provinces than nations, it presumably places them randomly and leaves some start locations empty as extras.

#specstart places a specific nation in a specific province, so if you want them to always start in a certain location, then this is the way to go. Otherwise #start is good.