Patch tear? is that the key hole at the back end of the blade? I never heard of it described as that but it makes sense. 

I have always wondered what that was for!

There was a revolt in India back when England colonized the country. The native men being trained to shoot the rifle where muslin and the pig fat I think it was that they used to seal the ammunition. The regular British solder in haste to load as quickly as possible would bite the ends off instead of a knife like this one. So the solders in training refused to put pig fat/meat into there mouth & hence I believe a lot of people died at the hands of the British?