Question: I am using Office Version 2206 (Build 15330.20230), the current version. When I am searching for an email it shows a message that maybe not all results are shown and that it is still indexing 127279 emails, many more emails than I have recieved since the issue occured. When I search for something it only shows results that more than a year old.

This problem occurs only since a couple of days, possibly since the last update from July 06.

Answer: 
I think some of the arguments missing is that it is convenient that a register can be divided into two parts which are easy to work with, for instance with smaller registers. Hence, for the intel architecture, you initially had 16 bits registers that were subdivided into two 8-bit subregisters, and then these registers were extended to 32 bits, keeping the least significant digits addressable as 16 bits register, and then to 64 bits. If you had a 48 bits register, it would leave an awkward 16 most significant bits part, and you would have to play with 16 bits and 32 bits subregisters... What a pain !

Moreover, when you multiply the contents of two registers, you need a register of twice that size (or two registers of the initial size) to contain the result. Having registers that cannot be combined two by two would make things complicated for arithmetic.

I guess this view is supported by the fact that, for addressing (and not arithmetic), the processors internally use other numbers of bits.
Generally, processors are referred to as x-bit, where x is the width of the data bus.

In rough terms, increasing the data bus size offers primarily speed as a reward...twice the bits, twice the data access speed. This is the ideal; some inefficiencies are involved (e.g., fetching 1 byte still takes 1 cycle on a 32-bit system, same as fetching 4 bytes).

As ctrl-alt-delor points out, there are some logistical advantages to stick with a bus width of 2\*\*N. The only restriction of following this pattern is that you have to double the width every time you introduce a wider architecture, giving a max access speed increase of 2.

And in the end, it's hard to justify a new architecture if it's not at least twice as fast as the old one.

Note that low end microcontrollers offer many exceptions to this rule, and the properties of audio and human perception have made 12 bits a popular width for DSPs.