Well, you got PDP, Echo: DA, Echo: Galaxy.
Off the top of my head, there's also the PVP zones, Tunnels of the unicorns if you didn't count them in the Paragon total, Rikti Crash Site, old Faultline, Midnighter Club, Fort Trident, The Cruicible, First Ward, Night Ward (so 8 for Praetoria), destroyed Galaxy City tutorial, the original Galaxy City (it's still there separate from the echo, I have a character logged off there), um.... Precinct 5 Tutorial, and Lord Winter's Realm.
There's also a few one-offs that could probably be removed and recycled. For instance, the special copy of Ouroboros they made for the wedding event.
And yes, the way zone IDs are allocated could be redone I'm sure. It's just a question of how much work it would have been and how many other systems had to be touched (Pocket D teleporter for one uses a static teleport to zone 83 in the power definition; there may be others).