Have one like this
I have one or two with a cheek cut down like yours. I believe this is the result of a dropped plane where the cast iron cheek broke away. The owner may have tried to clean it up and smooth it out leaving file marks. I acquired mine for salvage parts. How the cheeks extend from the body make them a natural outlet for the shock energy outlet when a plane is dropped. The brittle cast iron can then fractures along an arc.
“Whether you think you can, or you can’t, you’re right.”