I haven’t read the novel yet (gee, just how much longer the delivery is going to take), but based on the summary and what we already know from the OnS universe, I’m thinking that at least a part of the whole Michaela name deal is that those who receive that name are deviants, both as humans and later sequentially as vampires.
For Mika, his obsession with Yuu was mentioned to be something that normal vampires can’t understand, he also pretty much retains the more or less full scope of human emotions, and back before Mika became a vampire, although it wasn’t too visible, he seemed to be an oddball in that he fearlessly tried to take advantage of a high-ranking vampire (Ferid, obviously) and find a way for his family to escape. For a little powerless human child, it’s pretty damn heroic if you ask me, those guts, brains and resolve were way beyond his years.
Crowley is a deviant, too, being clear-headed enough to question the purpose of the crusades as a human (he retains this analytical trait as a vampire, thus his insight ability that you’d never expect from someone who, on the looks alone, seems like a bruiser but not thinker) and his subsequent realization that God and what people do under the banner of His name are two very different things, and that they’re basically on their own, no help from God. As a vampire, Crowley is suffering from acute boredom, which doesn’t seem to be common for vampires either. But what’s more, judging from the summary and spoilers, he has a purpose in life - to find the vampire whose fault it basically was that he had to become a vampire himself via Ferid saving him from death as a human - and he may say to Ferid that he doesn’t remember much of his human past, but I’ll be damn if he really doesn’t, because all points to him actually remembering pretty clearly even after all those centuries - moreover, cherishing his human past deep inside (and not wanting Ferid to know about it, preferring to just laugh it off, probably because it’s far too personal for him). Both are highly unusual traits for a vampire to have, especially considering that Crowley is not a new vamp like Mika, who stopped being human just recently, but at least 700 y.o.
And then, there is Ferid himself, of course. We don’t know his human past, but as a vampire, he’s basically the King of Deviants and walking eccentricity, very interested in humans and characterized by who knows how many traits that a vampire isn’t supposed to have.
So there you have it: imo, it’s pretty clear that all three “Michaelas” we’re aware of are special existences among both races, and this is probably part of the reason why they’re “Michaelas“ in the first place.