This might get you started....

http://www.flyertalk.com/forum/Forum35/HTML/005202.html

The numbers shown tell you that 4 tickets OR MORE are available for sale in each of those fare categories. I'm not an expert on this stuff, but I think Galileo shows a max of 4. On the NW system the number will reflect up to 9, when 9 OR MORE seats are available. When lots of zeroes are showing you know the flight will be quite full.