I dont know if this will help with a solution, but to fix one link all
that I have to do is:

Right click the cell
-Hyperlink
-Edit Hyperlink...

Then delete the year and month from the filepath box.

so: '\2003\MARCH\item_serial_mar_03_001'
becomes: 'item_serial_mar_03_001'

Interestingly the dialog box only shows the folders steps above, not
the complete filepath, which isn't a problem.

Idividually the problem is an easy fix. I was hoping for some useful
code that allowed me to do the whole worksheet in a click as doing
this 300+ times is highly inconvieniant. Ta again.