One more time - 5 cases
You have reminded me kindly that there were, in fact, 8 cases in the
earlier Indo-European languages. Smyth suggests that they were "lost"
(that is the 3 - ablative, locative, instrumental) in Greek.
It just seems to me that the world of Koine Greek grammars could benefit
by some clarification on this issue. It certainly isn't earth-shaking or
anything, but there is a difficulty when the technical grammars (BDF, MHT,
and Smyth) refer to five cases, while just about every intermediate grammar
on the scene utilizes the 8.