With the many cultures that have 'snake' symbolism including India (Naga) and even Europe, that,so far have not been mentioned. I think tying the engraved blade to a specific time frame/culture will be difficult.
Hopefully, the dimensions/spec. of the blade will be forthcoming soon, this would obviously help to assertain the knife's function ...and perhaps then 'narrow' the possible origin. I do hope the blade is not thin and flexible...would you need the protection of the crossguard whilst 'buttering' your bread
IMHO I still feel that the 'raised' spine is functional and not a symbolic feature to 'mimic' a Benin blade, which usually represents an animal form.
Regards David