The only reason I could think of to cut it that way, or to glue that in, is to create a kind of “break,” so of you are sliding your hatch forward, you won’t smash it into the mast.
There is no way to know if there was a similar wedge on the other side, because the forward end of the other guide is missing.
There is no way to know if there was a similar wedge on the other side, because the forward end of the other guide is missing.