I guess you're right. I worked in Santa Clara for 25 years but had never heard this.

The city ceased to exist when it was consolidated with the City of San Jose on March 12, 1968, following a 189 to 180 vote in favor of consolidation. The city's final census was in 1960 when it recorded a population of 1,174.[7] The United States Postal Service still recognizes "Alviso" as a place name. Mail is not delivered in Alviso, but must be picked up at the post office.

Do you know the names of any cardrooms that were in Alviso when it existed as a town, not just a place name? I'll see if I have any chips from there.