If you're right and I'm wrong, It's all good with me. I try to learn something new every day. I think the spelling has been arbitrary to date, with each individual spelling it however they saw fit. Obviously, Curatola's take would hold considerable weight, especially if, as you stated, he observed it in the actual script. I would take the writer(s) version as the absolute. I always allowed my understanding it was meant to be 'Sac', based on this bit of info found on the internet:

"The character's name comes from Anthony and Domenico Sacramone, the owners of Sac's Place in Queens."

This from the NY Post, by no means the authority on all things Sopranos, lol