I should've been specific....
Don't count the concept cars...just how many working, driving prototypes you think are in existence.
I misread your question anyway. I didn't count concepts, but I was thinking 5 in north america. I would guess about 7 in AU and 5 in NA
edit:
reason I say 5 in NA is because the leaked photo the other day. Someone at the plant was mad and said "they finally let us build some of these cars at the plant and this ******...... had to take this pic".
So I would assume that implies there is more than just that 1 in NA. I would think "some" implies more than 2-3.
And we seen at least 3 from the zebra camo ones. I would guess there must be more than those 3.
I would not doubt there are a few RHD units as well for the AU car testing.