the id's can only be tracked if that person has connected to an rtb server or has rtb, so if they never connected to a server with rtb or had rtb then they can't be tracked, for example my ID wasn't tracked until around 2010 and I've had it since 2008
Some keys are skipped and not created I guess the way the algorithm works.
I believe every key exists except 2-99, 666, and 1337