[sciurius]

Yes; that's what my code does.  Do you envisage any problems with that?

Mostly that it is a total unneccessary complication.

Yes, but I would argue that the usual interpretation is less useful in this scenario than the meaning I am proposing.  Otherwise you manually have to go through every single song and provide its last page.
...
Another approach might be to provide a simple Ruby / Python script which automatically calculates the last pages via the same algorithm and then outputs an updated version of the CSV file with those numbers included. ... But this two-phase approach is less convenient for the end user and I don't see any real advantage to it. Am I missing something?

A rule of thumb is that when you generate data once, and process it often, it is better to put the overhead in the generating phase.