The issue is this...
Word defines index entries using XE fields and optional referenced ranges.
InDesign uses index entry markers and optional ranges measured from the marker.
Considering insertion point entries first....
In Word the XE field contains index entry information. The location defines the page number in the generated index.
Sublety...
Using the Word indexing module, the XE field is inserted at the end of the selected text. This may cause the XE field for a very long entry to appear on the next page.
When these entries are imported to InDesign, location mapping is aligned.
A range index entry in Word references a bookmark. The XE field referencing the range can be anywhere in the document. If it's too far from the range then it will impact page number order in the generated index.
InDesign index entry markers define range starts. Range extents are defined as distances from the range start as paragraphs, characters and other measures.
For compatibility, Word XE fields must be at the beginning of the range.
When imported to InDesign, range information is lost and must be reconstructed. This falls to the Typesetter.
As I've gathered information about the Word indexing module and compatibility I've included it in the IndexExploit user guide. For compatibility, see page 51.
Barry Campbell