Just Nine Months

Watching this excellent and short video, I heard a very interesting comment made by Rothbard. I have also seen many people in internet asking about this "nine months' quote".

He was talking about the 1920-21 Depression and in 00:55 Rothbard said: 

"[T]he recession which was very deep, it was a real depression, there was big unemployment, prices fell sharply and there was a lot of bankruptcies. Was over in nine months."

I wondered where did he get that data? So I went to Fred II and this is the excelized result:
 

There you can see the peak before the continuos falling of industrial production. Production fell nine months before it starts to recover. This is what I think Rothbard could be referring. 

Vernon[1] and Friedman-Schwartz[2] confirm that the real severe part of the contraction took place in months or a year at maximum.