I totally get where you are coming from. I'm trying to think how to put this...I think I can more easily excuse nobody acknowledging he is back, if they even know he is. The Luke Cage mention wasn't super specific to him dying, I think it's just along the lines of "People will never know what Matt did under Midland Circle" or something. I can't really remember the Iron Fist one either, but I don't think it specifies him dying. Plus, we don't know what happens with Matt after Season 3, maybe he travels and no one catches wind of him being back (I don't believe this, I'm just making a point.) . I just feel like Luke and Danny's reaction, and Jessica Jones not even mention, of Matt is easier to explain away then a year or more gap between the Defenders and DD3. I know he was banged up, from you know, A BUILDING, but it's just a bit long. Especially since in the show they only use months and weeks. I think the only reference to years may have been Fisk's two years line, but I've only watched through once.