You are correct. There are 8 counties in the state that still permit inter-county transfer of the "base year value" set forth in Proposition 60 (wherein a property owner over 55 can transfer there property taxes on their personal residence to a different property, generally of equal or lesser value, within 24 months of the sale of their personal residence). There are limitations and specific conditions must be met, but it can save a homeowner $1000's every year when they move to another home. This was originally set up for moving within the county but Prop 90 gave counties the option of expanding this at their discretion.
The 8 counties that allow this are: Alameda, El Dorado, Los Angeles, Orange, San Diego, San Mateo, Santa Clara and Ventura. So a 55 year resident of Danville could sell and move to El Dorado Hills in El Dorado County, buy home for less than they sold for here and take their property taxes (based on when they originally bought their home in Danville) and apply them to their home in El Dorado HIlls.
My wife and I did exactly this only we stayed within Contra Costa. We sold our home of 29 years (with $2000/ yr in taxes) and bought a less expensive home in Walnut Creek and moved our $2000 in annual taxes to the new home and save over $3000 per year as a result.
if you have any questions on how to do this feel free to contact me at: firstname.lastname@example.org