It is well known that the major external differences between the A4D-1 and A4D-2 Skyhawks were the inflight refueling probe and the externally ribbed rudder. Also the vortex generator arrangement but that was much more subtle.
But here is A4D-1 BuNo 137821 with an inflight refueling probe:
Here is the first production A4D-2 BuNo 142082 with the solid -1 rudder and rudder damper on the middle rudder hinge:
Here is A4D-2 BuNo 142095 with the externally ribbed rudder but it doesn't have the inflight refueling probe:
These, of course, are extreme examples of flight test and very early production airplanes but they illustrate why model kit manufacturers might have trouble getting every configuration detail right.