Joker is really like the devil who appears out of thin air on that street corner before the bank heist. No name, no alias, no fingerprints (i just said that out loud like batman btw..FINGAAPRRINNNNTSS!), no dental records. I mean it's creepy. He gets locked up and then it's as if he vanished out of thin air when they take Arkhams patients and move them to Blackgate. The thought of them doing this but leaving Joker in Arkham alone...returning to the Asylum to find out that Joker is somehow gone as well. Very creepy indeed.
And that's a good interpretation. That 'Joker' as a name would be like taboo around Gotham. He caused so much crap, now that the city is doing well, it's almost like they're crossing their fingers as each year passes so i could buy into it. Plus TDKR wasn't a year or two after the events of Joker/Two-Face. 8 years is a long time. The Dent Act is a constant reminder and why Harveys name is brought up. The Batman killed him and he was around a little longer than everyone else. This is somebody who shocked the city with his appearances and people started to like him at some point then it's as if he betrayed them when he killed Dent and a bunch of cops. 8 years later there's probably still a mixed response especially since he dissapeared, there's no closure. And mixed responses causes discussion a lot more than just a psychopath who ended up being locked away forever.
That's why it never bothered me that they wouldnt mention Jokers name 8 years later. Even if it would have been cool.