Thanks for the encouragement winterkjm! I will post my full itinerary when I have it all figured out, the plan is to leave January 10. Unfortunately, I will be missing Archipiélago de Revillagigedo as well (forever, I guess, unless I take up diving).
Isla San Jorge (or Bird Island) from Puerto Penasco
: I was a bit doubtful whether it is in the core zone. It depends on how you interpret the map: there are islands colored in green (which definitely are the focus areas) and there are the borders of the much larger nature reserves (where Bird Island falls into). See https://www.researchgate.net/figure/Upper-Gulf-of-California-and-Colorado-River-Delta-Biosphere-Reserve-including-the-core_fig1_301600285.
But from looking at the size of this component (Upper Gulf of & Colorado River Delta Biosphere Reserve) as stated in the IUCN file - 454,591 ha of marine area - it seems that all is included. Also, it seems logical that if you want to protect the vaquitas, you need a large marine component and not just islands. In that case, the zone just extends to the coast west of Puerto Penasco and will include Bird Island.
Bahia Loreto may be another relatively easy one to cover the Gulf of California WHS (from Loreto). If I do not make it to Baja California, I will "do" Islas Marietas from Puerto Vallarta for this tick.