Are you really sure you’re not making progress? Measuring can be very deceiving since it’s almost impossible to place a measuring tape on the exact same place every time. I find the most reassuring way to tracking progress being the fit of my bras and photographs. Of course the photographs have to be the exact same angle, light and taken on the same day of the cycle every month since breast size changes naturally during the cycle.
The doctor who invented the Brava system said that every day pumping adds about a drop size of breast tissue growth, and that’s with the recommended Brava regimen which is 10 hours per day. From this forum and the noogleberry forum it seems many people do respond faster, but some might be even slower. If you’re an AA cup with no breast tissue to start with its going to take longer.
Since your 6 months in I’m assuming you know how to pump, but maybe you can experiment with different techniques?
Other things you can improve if you haven’t yet is calorie intake, blood circulation, massage and maybe get a hormonal test done just to be sure there’s not an imbalance hindering your progress?
I also want to point out that in the NBE world 9 months isn’t very long, the successful growers here did it for years! But I get the feeling, keeping the hope up is almost harder than the NBE routine itself.