creating an index for a book

[pvoyance]

I am using Microsoft WORD (any version is the same)
to write a book.
My files contains

Chapter1.doc
Chapter2.doc
.....
Index.doc

The starting page number of each chapter is input by hand after the ending
page number of the previous chapter.

In each chapter I created functional variable XE.... for index.


In the last file index.doc I use function variable
RD[....] to include all of the previous chapters.
The I created an index for the whole book.
The page number of index.doc is put by hand in the same way as the previous
chapters.

What bothers me is every time when I update the function variable of the index, the starting page of the Index.doc is reset to start from 1 instead of
my previous set number.

What is wrong with my usage? Thanks.