As I said, the Urban Legend retcon introduced some complications; Dick’s participation with the Teen Titans is one of them, just as Bruce’s participation with the Justice League was.
Personally, I tend to take the position that you should change as little as possible in a retcon, especially one that’s necessitated by someone else’s retcon. In the case of Tim’s origin, I prefer to keep him as an eyewitness of the Graysons’ deaths, but to supplement that with a right-place-at-the-right-time witnessing of Dick going after the mobsters on his own and Batman stopping him, as shown in Dark Victory. With that supplemental early encounter connecting Dick to Batman in Tim’s mind (and making his belief in Batman be based on first-hand experience), the years-later incident where he saw Batman and Robin on TV could easily be changed to seeing footage of the New Teen Titans in action.
In terms of retcons to watch out for, I’d also draw a sharp line at Infinite Crisis: when New Earth was created, we know that a few changes were definitely made (e.g., Superman’s timeline being revised to the Secret Origins take, and Wonder Woman being a founding member of the JLA); but who knows how many minor changes were made? In particular, it’s entirely possible that Infinite Crisis, Final Crisis, or both de-aged Tim by a year or two. Final Crisis is the more likely culprit in this regard.