2) The same idea of 'in between' has been applied before in the text in a similar way:
"Do you really think that, [...] if a thing's not wise, it's ignorant? Or haven't you found out yet that there's something in between wisdom and ignorance?"
"It's judging things correctly without being able to give a reason. Surely you see that this is not the same as knowing—for how could knowledge be unreasoning? And it's not ignorance either—for how could what hits the truth be ignorance? Correct judgment, of course, has this character: it is in between understanding and ignorance. (202a)
We can use a diagram of the same form as before to visualize this example:
Now, questions of knowledge, wisdom, correct opinion and ignorance aren't in the center of this dialogue. They're just used as examples and parallels, probably because the main speaker (Diotima) thinks that her interlocutor (Socrates) is more familiar with them. What is in the center of the this dialogue is the nature of eros. So how exactly are these examples and parallels used in order to give an account of the nature of eros?
 The distinction that is made here between knowledge on the one hand and correct opinion on the other is not discussed in detail. It's taken for granted as far as the discussion in this dialogue is concerned. On the dramatic level, Diotima assumes that Socrates is familiar with that distinction and accepts it; and sure enough, Socrates agrees to the analysis that correct judgment is in between knowledge and ignorance. On the level of Plato's philosophy (the philosophy that is dramatized in this and other dialogues), it's also taken for granted and discussed in more detail elsewhere (namely, the Theaetetus).