Thanks Llamabeast
I had been looking at the files with a hex editor and noticed that the 13th and 14th byte pair also represent the turn but it was a pain trying to use it. Eventually I found the --verify line and have currently broken my version in my attempt to read the .chk version. Ahh, the joys of a new language when you have no idea what you're doing.
I was going to look at it again today to try and see where it is failing.