I just have no idea how to distinguish those cases from "I'm not ok and I'm hoping you'll reach out and ask further".

I'm better at handling the social "OK" because it usually is OK to drop the subject; the social "no" to, e.g., "are you disappointed?" is a lot harder because the subtext is usually very important, and I have no way of getting at it without continuing a discussion that the other person might prefer to drop. At least with "OK" the real answer will usually come out if it's somebody who knows me and I have time to continue the conversation.