All these methods using [A-Za-z0-9] recognise 139 characters (with the Latin1_General_ci_as collation).

Now personally I think that's right (although it's a rather complicated pattern to use for the job), but I have met a lot of people (all Americans, I think) who claim that there are only 62 alphanumeric characters and lose their cool when anyone suggests that there are more; I guess these people must insist on using the bin collation instead of a dictionary one, and use the complicated pattern because the simple one delivers 75 characters even with the bin collation.