I don't live in California, but AFAIK prescriptions aren't per order. You get a medical card via a doctor's recommendation, and then present that card to become a member of a medicinal "club" (which probably requires validation with the state that you are properly licensed). If I understand correctly, Meadow then interfaces with these clubs to provide expedited delivery to their members. Essentially, the hard verification work has already been done since only members (with medical cards) can order from the clubs Meadow delivers for.
As of a couple years ago (the last time I was there), you can actually call the club and have them verify you at the time of delivery (eg, you show your recommendation when the driver arrives, before any transaction is made).
Doctors who issue recommendations have sites or phone systems that can be used to verify a patient 24/7. VaporRoom and other delivery services use these and then check the paper copy + id upon delivery.