9N and 2N were very similar, however the 8N was a much different animal. Counting them as one model for puffing up the numbers isn't quite right. If that's OK, the Ferguson shound be able to include the TO35/MF35 along with 20/30 numbers to be fair.
From what I've seen and read, the original "Fordson" (model N???) built in the teens and 20's was the highest produced single model ever. Don't have numbers handy, but there were an astronomical number of them built.