How interesting! I just did a random Google search for each of the classmarks you gave and they both came up with results from the Institute of Classical Studies Library at the Joint Library of the Hellenic and Roman Societies. I therefore searched for that and here is some information for you http://w01.icslib.wf.ulcc.ac.uk/about-collection.htm
If you scroll down you will find a paragraph all about their classification system! I hope that helps.