S in a Chevron denotes tube sourcing from the Schilling forge. Indeed, Wilhelm Kelber did use a script WK but not like this one. August Wolf would not have sent his wares to the Z-M proofhouse unless there was a renovation @ the Suhl proof facility, which was about 3 years later. Z-M used a ledger number as the last number in their proof sequence & it notes the total number passed for that month.

Cheers,

Raimey
rse