[CJE]

Something I don't understand.
According to the usual JNAF practice, the first digit of the Model designation was changed when a new engine was installed and the second digit when the airframe was modified.
AFAIK the difference between Model 11 and Model 21 lies only in the latter's manually folding wing-tips. Thus, this version should have been called Model 12 and not Model 21!
Where do I go wrong?
Thanks.