Hi, thank you for replying and for researching/considering the changes you are making. 

The wiki page for the cork tag is https://wiki.openstreetmap.org/wiki/Tag:surface=cork although it doesn't seem to be linked from the surface values page. I've made some tweaks to the Castle courtyard in Lancaster in https://www.openstreetmap.org/changeset/160071618 to reflect this and previous discussions. 

I've also split the track in Millom in https://www.openstreetmap.org/changeset/160071000 and updated the track_type tagging for the section which looks to be asphalt, and removed the surface value from the section which doesn't look to be asphalt. 