Are you using Word 97? My experience is that in this
version only the current level number is visible in the
Number format box, even if higher levels are included.  
For example, it displays

..1

for the third level of a legal numbering numbering scheme.
Note that all the separators (periods) are visible!

Also, if you move the insertion point so that it is
positioned between the separators, the Numbering dialog
box does indicate which level should go there. For
example, if you place the cursor between the two periods
in the above example, the dialog will show that level two
numbering is included there. Inspite of this behavior,
numbering looks correct in the document.

If numbering doesn't display correctly in your document,
it's probably easiest to rebuild the entire outline,
starting at the top-level style. (This applies even if
you're using a newer version of Word!) For more
information, see

www.shaunakelly.com/word/numbering/OutlineNumbering.html

Stefan

Unfortunately, I cannot help, but it is nice to know that
someone else in the mworld has he same confusion at the
operation of the "Customise" function in Outline numbering

Michael A, Australia