Another thing to consider....I was originally told (it may have been in the original Ebay sellers description,witch is not too reliable),that it was a cutter ffor "rope" type glazing,but the era of the knife - it does not make sense,I don't think they had a type of material in a roll form. It may be like a string,or cord cutter,Perhaps they used a type of material like a cord,to tuck in between glass panes and thier frames,back then.That could be possible
If it is a Glaziers knife
Edited in - It could be,(BL seems to suggest it was a novelty knife),that it's design was like a "handymans" knife,and that hole is for a wire stripper
So,Glazier,electritian,baker ( string cutter),and waiter,all could benefit.
-Vince