4, 5, 10

[Constantinus Philo]

οὐδ᾽ ἂν σέ, ὦ Κῦρε, περὶ ἐμοῦ οὕτως ἀπρονοήτως βουλεῦσαι,
this inf stands for aor ind with an expressing unreality, doesn't it?
εἰ δὲ Κῦρος οὕτω γιγνώσκοι, οὐκ ἂν ὑμᾶς, ὦ Μῆδοι, ἐθελῆσαι οὕτως ἔρημον ἐμὲ καταλιπεῖν.
The first opt stands for imperf in oratio recta, and again, inf with an stands for unreal ao.

[phalakros]

Yes, that’s right, though γιγνώσκοι is ambiguous between representing pres or imperf ind.

[Constantinus Philo]

in 2623 Smythe says that all past tenses with an remain unchanged. So maybe an should go with ᾤμην?

[phalakros]

It’s true that past indicatives in subordinate clauses usually do not become oblique optatives in indirect discourse so as to avoid ambiguity. There are exceptions, though, and I think mainly in Xenophon. Rereading, however, I would actually take it as representing potential optatives not past indicatives. That is, direct speech would be:

εἰ δὲ Κῦρος οὕτω γιγνώσκοι, οὐκ ἂν οἱ Μῆδοι ἐθελήσειαν…καταλιπεῖν.