Hi Franek, you seems to have missed a bit of the sentence
:
If they hadn't introduced the E-7 or E-4 references which were useful on a tactical standpoint (...)
I was saying that the E-4 and E-7 denomination were introduced because of tactical change either armament (E-4) or range (E-7) and that if they hadn't chosen to do so you'd have had E-3s with a whole range of differences between them. I was just trying to make a point on the E-7 being an E-7 just because of a choice of designation based on a single change of tactical importance, sorry to have been confusing.
No i believe all surviving E-3 were at some point upgraded to E-4 status, it was not too long a task. Data plates were usually over stamped with the new designation at the workshop. But i'm not so certain about the E-3 to E-4 upgrade since the modification could have been done in the field and i'm not certain they overstamped there.
I have seen plates of E-1 converted to E-3 and even E-7 but no overstamped E-3 dataplate with E-4 instead.