I can't tell from the context of your comment whether you believe the monthly inflation figures are inflation that happened in that month (the "one month's wort

I can't tell from the context of your comment whether you believe the monthly inflation figures are inflation that happened in that month (the "one month's worth of inflation was X%") or if those are annualized figures (the "one month's measure of an annualized rate of inflation"). If you are of the belief that the monthly inflation figures "stack", you are saying inflation is much higher than the 18% in 2 years that GP reported. If you are not of that belief, then the figures you cite are fairly consistent with the 2 year rise in prices being in the +18% neighborhood.