They never "hit" one million. The addition of the V was made because S&W's numbering machine only went to six digits, so when they reached 999999, they decided to add an initial letter (the "V" for Victory) which would be put on all guns when the frame was made (the serial number was stamped later). Sometime in December 1944 at about serial V769xxx, when the new hammer block safety was added and the "S" added to indicate that change.*
They reached VS811119 when the Army contract ended and production continued into the post-war period without the "V", starting with S811120.
*Revolver frames already completed and marked with the "V" had the "S" added ahead of the "V", giving an "SV" prefix. Revolvers fully completed or called back for the modification had the "S" added after the serial number. Frames made after the change have "VS" numbers.