My rarest Pen-Knife - an OIO by Clarke, Shirley and Co

This penknife was given to me by my father, who had received it from his father. It has a black, rough steel handle (cast to look like bone or wood - 78mm long, width of 10mm tapering towards the back at 17mm); it bears the mark "OIO" in relief. The blade is short and stubby (60mm x 10mm) and stills holds a wicked edge (even after over 100 years!). The blade carries the name of "Clarke, Shirley and Co, Sheffield". The blade also has the "OIO" mark.
I tried to get info on this knife for decades, but no-one knew anything about it or the history of the company.
Enter the Internet: still didn't have much luck. But recently - after a long and hard search - I found a copy of a book from 1879 titled " The Illustrated guide to Sheffield and surrounding districts". This had an advert for "OIO", which I have included. I also found one obscure reference to the fact that Clarke, Shirley and Co, sold out the OIO trade mark to "Harrison Fischer" - but no date was given. Also, another obscure reference stated that Clarke, Shirley and Co - "cutlers of Eyre Lane and Howard Street" - had won a First Class medal at the 1878 International Exhibition in Sydney Australia, which backed up the advert claim.
What I DO know so far is this:
(1) definitely not earlier than 1879 - this was roughly when W Shirley became Clarke, Shirley and Co.
(2) Could be between 1879 and 1892 and even later than 1892 - Clarke, Shirley and Co still had the OIO trade mark in 1892. (got this from a hallmarks book).
(3) Doubt whether it was much after about 1920, since my Grandad was born in 1905 and would have been a teenager when he got it from his dad.

If anyone has ANY idea of how to date this knife, please let me know. Much appreciated, Garth

PS: I have also identified the possible source of my knife: There was a World's Fair held in Kimberley in 1892; since Clarke, Shirley and Co had exhibited at other World's Fairs, they may have done so at this one. My father and his forebears lived in Kimberley for nearly a 100 years. My great-Grandfather could have visited the Fair and possibly bought the knife there (he was quite a prominent personality). But all this is conjecture at the moment. Once I locate a copy of the 1892 Catalogue, I will try to verify this. Unfortunately, the only copy I have is located in Kimberley museum.....1000km from me!!