Cotterill padlock key

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I would like to get some info on the Cotterill numbering and size difference for padlocks. See attached picture of 3 padlock keys I own and all which are different sizes. The larger ones looks like a standard padlock key the other too particularly the really small look to small for the locks I have typically seen?

Can anyone tell me what each key would like have fitted?

Also I have Cotterill keys with letters from A up to W. What year do these represent and is each letter a corresponding year?

thanks