These are my latest find

Ear notchers ?

I'll go with a sheet metal tool to bend over some kind of rounded tab.

Perhaps a farriers tool?

not ear notchers no gap to put ear

It looks like when the handles are squeezed together, the jaw opens - so maybe the "working surface" is the outer round edge?

So if it made a notch in thin brass, but didn't remove material. There is seam using a notched overlap that is soldered. Seen this on "How it's Made" making brass musical instruments.
But the notch would not need to be as deep as the tool is. So might not be the right answer.

Can anyone shed any light on 5 Y's Patent - I couldnt find anything

I should have noticed the hinge direction.  My first idea would not work.  How about a tool to hold or expand an oval ring for some reason.

Hinge direction - yes you are right, (I think) they are more for expanding something rather than cutting as they work the other way round. Also holding the handles together makes a nice taper leading up to the "head" Maybe they are medical ? or Vet related ?

So have I beat you all ?

 no, you have not beat them, they never give up here.

possibly for stretching a rubber band or o-ring prior to slipping it over ???   

Quotepossibly for stretching a rubber band or o-ring prior to slipping it over ???

Don't think so, when you release them there is no room for whatever you are sliiping something over.

I have been scouring the interwebs and haven't found a match yet.

I had thought about rubber bands, but i think it might be more like a circlip with a gap in it ?