This is normal -- as noted at
http://Help.KVSTool.com/#Interpreting:
"Depending on the airline, cabin and the GDS system used, the maximum number can be one of the following: 9, 7 or 4."
...
Understand LH only release up to 4 and UA releases up to 9, and .....
But why would some flights on the same airline, day and cities show 4 max and some show 9.
.... You can also use the [Availability/ETR] Method, which is currently showing F9 Y9 for that flight.
Very awkward method, no easy way to see the entire (paid) fare class set.