Unique autonumbering, need full page count for book

I have been searching all over the Internet.

I am trying to add a variable that would do a total page count of the full document.. while this is not unusual for a request, the book is not a continuous numbering system.

For my cover I need a total number of pages included in the book. However each chapter has its own unique set of numbering.

For example:

Cover- 1 page

TOC- 2 pages 

     Where the page number generation for this chapter would be done under numbering, using the "First Page #: 1 Format: Roman (xi)"

Chapter A-  this has 10 pages total, but the page numbers are a supplement to a previous edition, and would be pages 13-23. Where the page number generation for this chapter would be done under numbering, using the "First Page #: 13 Format: Numeric"

Chapter B - This has 11 pages total, same as above, but would start at page 40.  Page number generation for this chapter would be done under numbering, using the "First Page #: 40 Format: Numeric"

If I add up the total number of pages for this document, it would be 24 pages total.

I would need a way to count each section and add a variable to the cover that would say something like "This document contains 24 supplemental pages for XYZ document" Where 24 would be a unique variable that would change as more pages are added to the supplemental document.