John Martini - you are SO RIGHT.
I discovered in later Census reports, my paternal grandparents did not live above the grocery store at Castro and Jersey after a certain date. Phone directories showed my grandmother was widowed, lived at a nearby home about a block away, and later in a home just off of Geary, with her son who was my Dad, his son, and her "spinster" daughter Mabel.
I was always bewildered by this change of homes until I heard from my (WNP discovered) Quinn cousin - who explained that the Depression ruined the grocery store, my Grandfather died, and my Cousin's Dad (a son of that Granddad) supported the family until they were able to carry on independently.
As that TV Ad likes to say...
"The More You Know."