Where are you seeing numbers like that? My guess is that you're either seeing 1) PCGS/NGC populations or 2) PCGS populations of a certain grade/PCGS populations of coins graded higher than that grade.
One of my freinds is selling off a bunch of his coins, almost all are PCGS: http://forums.collectors.com/messageview.cfm?catid=7&threadid=727267 I'd ask him, but I don't think he is online right now..lol stainless
In the first coin he shows 1832 1/2C XF40BN, pop 17/249 it means that there were 17 graded that were the same grade, and 249 graded that were higher. You then have to go to the PCGS population page and see the total graded was 284. You can look at the PCGS label on his coin and the first part of the # 1159 is the coin ID number on the population page, the .40 is the grade. Often one does give both NCG and PCGS pops I try to give such info also , and try to indicate whether PCGS or NCG such as in this listing http://www.cointalk.com/forum/t57301/ Jim
I believe usually the first number is the number of them that received that particular grade and the second number is usually the number of them that graded higher. I think Heritage gives that info for PCGS and NGC in their listings.
