Not sure of your question. I've driven in CA. the last 4 years, with my 99 DP and never seen any problem with getting fuel or any reference to upgrades being required.
Now if your moving to CA and trying to register an older diesel , that may be a problem.
Only thing that you really have to watch is the all vehicles towing speed limit. They really enforce that limit.
Commercial Vehicle's may also have different rules, any transport truck entering CA. may be required to be DEF emissions compliant.