The number is unquestionably an undercount because it represents only those officers whose licenses to work in law enforcement were revoked, and not all states take such action. Full Article
Related
A 50-state look at officer decertification for sex incidents (on CA RSOL)
Sex-offender cops exploit broken system, AP investigation reveals (OC Register)
Same AP Article on
Another related article more specific to California cops
http://www.ocregister.com/articles/police-690100-officers-officer.html
Hundreds? It should probably be more.