The others are all various forms of coach fares. They may not all be available for sale on your flight. Some are for award travel, travel industry fares, etc. Y is a full-fare unrestricted fully refundable fare. The rest have some restriction, usually increasing as you go down the line. I think AS uses T for webfare availability. It doesn't mean that 7x the number of fare codes are available for sale, it means that there are at least 7 seats for sale. There may be 100, or there may be 7. Once you see Y and B reading less than the max 7, you can be pretty sure the flight is oversold.