EF will give you the number of seats the airline is prepared to sell in each fare bucket (with a maximum of 7 in Y, 7 in J and 4 in F cabins). Those numbers are in my experience quite accurate. But Y9 can be 9 seats available to sell, but also 109. And Y9 B9 does not mean 18 seats minimum, it means a minimum of 9 seats that they will sell either as Y fares or as B fares. Etc etc. There is a good amount of interpretation needed.