Not true - I have had several bezels that are too tight or loose which are easily adjusted by an experienced watchmaker.
I used to naively think I could just pop one bezel off and put another on, but in real life it only works about 50 % of the time.
So from experience, I can say that bezels and cases each have small, very small variations in size, and I do not believe there is any nefarious reasons for this variation.
I have not yet had a bezel case combination that a watchmaker was unable to fit together, (that I had not).
If you are doing this at home, then if you do not hear that magic "click" as it seats, be afraid.
I must say since returning to the first world, and access to a watchmaker, I have not changed a bezel myself.
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