As I recall, the flashback scene in "The Ride" where Christopher tells Tony that Adriana is working for the government was actually filmed for "Long Term Parking."
https://www.youtube.com/watch?v=dIH40bTNPZ0Starting at 2:05 to 2:55, you see Tony get very angry and upset, and for a good reason. Christopher was much more chatty with Adriana about the business, and who knows what she picked up when he was abusing heroin. Whacking the two of them would have been a good story line, but I wonder what the blowback from the FBI would have been if both were disappeared at the same time.
