Ah, that's interesting.
Well, what do you want to do with these girls?
Personally, if I've stopped talking to a girl, I basically just do not want her in my life anymore.
So yeah, when I see her, I will be cordial, but no more than that. Just don't want to give her any ideas.
If you ghosted these girls, then changed your mind later, and run into a girl you decide you'd like to start things up with... me personally, I think I'd give her a little warm "Hey, how've you been?" then if she's friendly do a "We should get drinks sometime" just to feel out where she's at. If she responds well I'd see if she was down for something there and then. If it's cool-ish I might just tell her I'd message her. Then I'd put it on ice for 4-5 days before shooting her a message. If it was a social venue where we were all standing around socializing, I'd probably swing by once more before leaving to see if she'd warmed up at all. If not, go back to what I was doing. If so, try to get something going on then and there.