Most of the time they cut off the excess digits soon after birth if it is possible, so there may have been more cases then you knew about. My father was born with twelve fingers, and they cut off the extras at birth. He didn't talk about until my mother was pregnant with me. And yes, my paternal grandmother smoked, but then so did my other grandmother and she gave birth to four ten fingered children.
"they cut off the excess digits soon after birth"
Really?
"she gave birth to four ten fingered children."
Sounds more like a genetics thing than a result of smoking.