Like, the differences in the 1991 basket to the 1992 basket are pretty small (please, someone, double check this). But the differences in the 1991 basket to the 2019 basket are larger, for example.
So it would seem to me to be a bit silly to have to update the prices of the 1991 basket all the way to today, especially when you're updating the 1992 basket as well, and every other year.
I'm not a CPI expert person, so if there is someone that really does understand these things in depth, please chime in!
A "normal TV" now is a smart (spit) TV which compromises privacy and viewing experience and durability - but which is sold massively cheaper than a plain TV as defined perhaps 6 years ago. You have to dig hard to find a plain TV and it's more expensive. Do you count "smart" as a positive hedonic feature? Or do you count the effort necessary to find a plain TV in the price increase of a plain TV? Do you compensate for much other price increases just because a "normal TV" is now much less expensive and (allegedly) more hedonic?
Part of the challenge is with how frequently they decide to change the basket of goods. If the basket was largely stable over time we would have a pretty good estimate simply by aggregating annual data, especially if they focus on staple consumables that don't change drastically over time.
They provide their raw data [1]. You can reconstruct the index however you want. There is an entire industry of consultants who create custom benchmarks for planners.
For personal purposes, your metropolitan area's CPI is a better metric to watch than the national number.
At some point, even the long-term index can't be constant.