We had a similar break on a vintage Brooks my husband had on his old Schwinn. (I think it's a B68, but I'm not sure -- that style, anyway.) Unfortunately it broke very dramatically at 2 o'clock in the morning when we were miles from home. He rode home standing up because he is nuts (and possibly he was a little tipsy).

That one did not have a cutout but it was probably 30 years old. I am really sorry this happened!