From Ambush Master's above link to the crucible steel website.....
It appears from quickly glancing at the pages that the other two forms would be very difficult to resharpen in the field. I am sure the expert in these matters will give us the complete scoop.
S-60V
http://www.crucibleservice.com/datash/dsS60v4b.pdf
Typical Applications
Long-wearing Specialty Cutlery
Industrial Knives, Slitters, and Cutters
Pelletizing Equipment
Wear Components for Food and Chemical Processing
S-90V
http://www.crucibleservice.com/datash/dsS90v7b.pdf
Plastic Injection and Extrusion Feedscrews
Non-return Valve Components
Pelletizing Equipment
Gate and Nozzle Inserts
Industrial Knives, Slitters, and Cutters
Long-wearing Specialty Cutlery
Injection Molds and Inserts
Wear Components for Food and Chemical Processing
Bearings, Bushings, Valves, Rolls
Gear Pumps