I get the impression that there's some special interpretation of okumuş değil, as opposed to okumamış. Could someone explain it?

Also, if relevant after that, is it an anterior or evidential/mirative -mIş?

(In Kyrgyz, a plain anterior negative happens to have a similar structure, окуган эмес, whereas an evidential/mirative (also anterior) reading is structurally more similar to okumamış: окубаптыр.)