The 9.5% is some standard number I have been using for a while, although Its old and I know its not exactly correct. I haven't bother with it much, because of the VIRTUAL SUPPLY that you have mentioned above, that is dependent on the stablecoin HBD price, and its getting hard to calculate the exact inflation number, cause it basically changes daily depending on price :)
Overall I agree that 8% is probably closer to the real inflation number than 9.5%.
Also the APR calculation that you point to, taking into account that not all the stake is vested is more exact. Thanks for that.