That is correct. You are subject the county laws limits but no less than default state limits.. per California medical cannabis patient in the household. That's how real grow co-ops are formed.. one big happy family.
under SB420: a doctor/physician can also recommend a higher amount (plants/quantity) if needed/requested by the patient inregards to medical use/amount needed on a daily consumption.. blah blah
but you should consult someone who is well versed inregards to medical marijuana laws