John mostly covered it, and don't give up, and you may not have to discard your past work, but you should be careful, especially of older quakes. If the depth is 33.0 or 10.0 or 6.0 km on more quakes than you would expect by chance compared to 10.1 or 5.9, then be suspicious that the depth of the quake was set by the location program. I put a whole bunch of quakes into 3D for Santa Monica Bay and there were so many at 6.0 km that any figures made showing these were probably unpublishable. But, these included quakes from the 70s, 80s, etc. But, today, I still see global quakes on the NEIC pages where it says something like: depth set by location program. So, John's comments on PDEs being pretty good may only apply to California and other areas with dense networks.
Chris