I am not familiar with the module but in the docs it says:
Spaces, symbols and non-printable characters are only considered for splitting the string into its parts but not for sorting. For instance foo-bar-42 is broken in three substrings foo, bar and 42 and after that the dashes are ignored.
For the examples you give the sort order would then be:
 
P007BYUM
P007YUM 

 
P007Yum 
P007bYum

 
P007byum
P007yum 

 
Which to my mind is correct. You might be able to use some variation of the Schwartzian Transform to achieve your desired output.

In reply to Re: Sort::Key::Natural sorting discrepancy by tangent
in thread Sort::Key::Natural sorting discrepancy by cr8josh

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