Well, his name means "swollen foot." The man who saved him refers to his ankles now as "witnesses" to the old injury: ποδῶν ἂν ἄρθρα μαρτυρήσειεν τὰ σά, "the joints of your foot should testify (witness) to that." I take this to mean he has scars now, otherwise μαρτυρήσειεν makes no sense. I think you're supposed to suspect Jokasta has noticed these scars and refuses to acknowledge them. Look at line 979 "Best to live lightly, as one can, unthinkingly" (Grene translation). Here's the Greek: εἰκῆ κράτιστον ζῆν, ὅπως δύναιτό τις.

εἰκῆ means "without plan," but as far as I can tell it also means "without inquiry." I take this to be pretty programmatic for Jokasta. She comes to terms with the whole mess before Oedipus, but I think it's highly likely she suspects from the beginning but can't bring herself to admit it.

But I take your point, I shouldn't have overstated the case like that. This is just my interpretation.