If you are going to include shadow inventory, why not go all the way and include all houses in existence ? The average person moves every 5-7 years, so they will eventually be on the market. Even those who think they can hold out forever cannot. They can't hold on forever because they will eventually die, unleashing these houses on the market. Add these to the potential foreclosures and you get about 34 years of inventory in San Diego county. So, the real potential inventory is much larger than these predictions.

FSD, I think you're underestimating the real potential inventory.  Remember that home builders are always building new homes.  The more demand there is, the more home builders will build.  So the real potential inventory is essentially infinite!