You're describing the method they used to try to (roughly) "track the cost of living". You can argue that it is or isn't doing a good enough job in terms of th

You're describing the method they used to try to (roughly) "track the cost of living". You can argue that it is or isn't doing a good enough job in terms of the choices made but that's specifically what it's doing (and while it may not be doing it well enough, it obviously does need to be done based on sampling not based on producing an exact % for each individual that the things they bought over the past year have increased). (You're not the person who wrote "neither RPI or CPI try to track increases in the cost of living", but that's the context of this comment chain.)