Some, like Dyre the Stranger and Caradog, simply aren't there and others are extinct when in vanilla they still existed (Sassanid one comes to mind.
I wasn't in the discussion with regard to the Caratacus bloodline, but I can answer the remaining 2 there: compared to other semi-mythical figures like Rurik, Dyre the Stranger has no comparable historical support to warrant his own bloodline. He wasn't revered as a progenitor like Rurik was. If anything, the Dyre bloodline seems like yet another attempt by Paradox to give him staying power by giving him extra opinion boost from Slavic pagans, on top of his Genius and Grey Eminence traits.
As for the Sasanian bloodline, during the CK2 period the lineage became a staple lineage that many dynasties claiming pre-Islamic prominence added to their lineage. The Bavandids are a good example of this, whose Sasanian lineage appears in later genealogical works. I gave them their own bloodline instead, so as to note their prominence among the Daylamites.
Is there a list of all bloodlines in HIP somewhere, preferably ones in use? I'd be very interested in perusing it for interesting characters to play.
There's no list, but you can take a look at the bloodline files found in HIP folder\common\bloodlines.