When I took Latin in high school, we learned that there are 7 cases -- of which two (vocative and locative) are used only with certain nouns (in classical Latin, there are only four or five nouns that have a locative case at all, if I remember correctly).
But for the five main cases, some of them had multiple functions, and we had to memorize the formal names for these functions. For example, we didn't simply learn that there is an "ablative case"; we were taught about:
Ablative of Place Where
Ablative of Place From Which
Ablative of Instrument or Agency
Ablative of Accompaniment
Ablative Absolute
...etc.
To me, this makes more sense than treating each of these ablative functions as a different падеж -- since, after all, the ablative singular of gladius (sword) is always gladiō regardless of whether you want to say that "there is blood ON the sword" (Place Where) or that "someone was killed BY the sword" (Instrument) or that "he traveled WITH his sword" (Accompaniment).
So, in the case of Russian, you could teach the Отделительный and Ждательный functions as "Genitive of Partition" and "Genitive of Antici...
...
...
...pation" (or something like that), rather than as entirely different cases from the Родительный.
PS. Regarding the звательный падеж, are there any examples at all other than Господи and Боже?