Fairbairn dagger question
I recently came across a replica of a Fairbairn-Sykes dagger, and it prompted me to look through some of my old WW2 combatives books, specifically Get Tough by W.E. Fairbairn, Combat Use of the Double Edge Fighting Knife, Kill or Be Killed by Rex Applegate, and Arwrology by Gordon Perrigard. At first, I thought that they all used the same type of grip (the foil grip), but it looked like there's actually two variations of it- one where the thumb is held in line with the edge, and one where the thumb is held in line with the flat of the blade. This one actually feels fairly natural with the original style handle, like this one:
in Applegate's grip and knife style, the thumb is definitely held in line with the blade, which I think isn't such a good grip but I get why he picked it. He used a thicker handle with a wider blade as well:
Are these actually two different things or am I just seeing things?