Hello Ian, I am going to have to agree with Kai, I just do not think that this is a ground down rengong either. IMHO this dagger was made to be exactly how it appears now. 
 
Kai, Unfortunately there are no markings on the blade anywhere other than rust staining and sadly pitting from being neglected over the years.  
 
Best, 
Robert 
 
PS  Kai, is this the area you were asking about?
		 
		
		
		
			
		
		
		
		
		
		
		
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