Hidden Intermission
The redundancy of the classical stems, and the fact that they don't cover everything about modern japanese conjugation without additional rules, is why the classical categorization is not used much anymore, except as a reference. The names it introduced are still used though.
Alexander Vovin, a salient academic linguist, considers the 未然形 form to be a figment of structuralizing classical japanese grammar. I think he's on to something, which is the reason I translated it as the "none such" form. The best part is "none such" is valid translation of 未然 if you think hard enough.
The only reason I named the 已然形/仮定形 form "some such" instead of "hypothetical" is because the stems on their own don't do much in modern japanese, and I wanted to avoid implying that it acts hypothetical on its own. In modern japanese, the "none such" and "some such" forms are basically incomplete and expect something to be attached to them.
There are other reasons to be careful with classical japanese grammar.
Japanese school grammar cares a lot about the classical bases, and they have their place in the modern interpretation of classical grammar, but they're not all useful anymore.
I should emphasize that the 未然形 has real uses of its own in classical japanese. The contention comes from conflating all -a forms of (back then) 四段 verbs with the 未然形 category name, which is named such because of a particular use of it. Modern linguistics treats categories as things that happen when you use words, or as features of "universal grammar", and applying categories too widely causes a lot of problems when grammar people try talking to eachother. The 未然形 category is a legitimate description of a real grammatical feature of classical japanese, but the name doesn't fit all uses of the stem.