Gentlemen,
For years myself and a few close friends have referred to the area that you are pointing out as the 'notch.' It means so much to so few that to expose it now would be a travesty. The notch is there only when it is there and at times it is not. Notchless blades are more common, of course.....why? Because they don't cause you to pause and ask, 'what is the notch for, who put it there, why the sporadic issue of this pointless missing part of the blade. The notch can make some men weep, others throw their heads back and bray like donkeys when they see the notch.
Stranger, if you see me and you see the notch, don't say anything and we'll be even.