CA corporation filing requires either the SOS number (12 digits) or the Corporation number (7 digits).

SOS numbers begin with the year of formation (either 19xx or 20xx, for now), thus SOS numbers begin with either 19 or 20.

When a corporations files its articles at the SOS, the articles would be endorsed by SOS and a seven digit number is assigned.  That is technically a corporation number, though some would consider it an "SOS" number because it's assigned by the SOS.