Not trying to be dense, and I get just module swapping as a repair technique.
I was aware of differing things to look for in cassette wear, but was asking about what might be happening that would not be readily apparent.
Modern cassettes have a lot of varying tooth geometry, making things less conspicuous.
Just looking to understand better what the mechanism of failure is.
Bulk module replacement is , um, inelegant,. It at best can exclude components as a cause.
Skips and mishifts may be hard to distinguish and reproduce.