That would be about right for an older STK-S2 Hot Stack. Duncan lists 20.60k, but that would be within excepted tolerance.
Edit: The Classic Stack (STK-S1) and Hot Stack (STK-S2) are the same coils. The Classic is A2 magnet and the Hot Stack is ceramic magnet. So it could be either one just going by DCR. The sticker suggests that it might be the STK-S1 Classic, bridge, wound by Connie Rocha.
Although, Connie did singles. It might be a poorly stamped "O", which would be Oti Mora, who wound stacks.