Here is the deal...as I understand it.
Prop 215 never set a limit, somewhere along the way, I think it is written in SB 420, (LEO needs to know when he can bite!) that the default 12 veg/6 flower be used and local governments could set higher limits.
This (SB 420) was challenged because it limited an individuals access to the amount of medicine needed.
I believe...the case is still tied up in appeals, but again here is the deal.
Could you, if caught with more than the local legal limit, argue your case and win? Probably...there is now even precedence (a legal reference to a legal ruling on the same subject)....However, the pigs have already stolen your garden and all your equipment. If you are lucky you have rich family or can sell your car to stay out of jail and pay your legal fees.
The limits are what law enforcement is using as a guide.
Disclaimer: The "Cannabis Climate" (I want credit if this catches on) is changing rapidly in Ca., and I imagine even in the conservative counties (like mine) the D.A.'s are reluctant to even bug any but the largest gardens following Obama's directive to the Justice Department to stop MMJ raids.