Pertinent to this post:
Since the PPA has no inkling of what the actual supply of any of their permit zones actually is, they routinely issue far more permits than spaces that can possibly handle those permits. Anecdotal evidence (courtesy a certain foulmouthed blogger) suggests, for example, that PPA Zone 4 currently has ~2x the permits its physical constraints can possibly handle.
Their ignorance--abetted by the fact that one has ever found a way to assess onstreet supply (until now)--is the only way they can get away with this. The implicit guarantee of a permit is that you are entitled to a place to park in the area where it's issued; if you have more outstanding residential permits than residential spaces, you've reneged on that implicit guarantee. Hint hint.