How to insert page sub-numbers in a word document

I can't think of an automatic way to do this, but the following may help.

Put a next page section break at the start and end of the additional pages.

On the last page of the 'first' section in the body of the text. Insert the following field structure at some suitable location.

{ SET X { PAGE } } using CTRL+F9 for each bracket pair

Open the footer view and unlink the three relevant sections.

In the 'second' section footer enter the following field structure

{ X } - { PAGE  \* ALPHABETIC }

in place of the existing PAGE field. Restart the numbering from 1 in this section.

In the 'third' section i.e. after the ABC etc section again restart the numbering at 1 for this section and add the following field structure

{ ={ PAGE } + { X } }

Note that this will only work for display purposes.

Did you do something to cause the { SET X { PAGE } } filed to be updated?

I am not sure that screen shots will help as the fields to be inserted are exactly as Graham detailed.  However, if you send me an email message, I will send you a document in which such a numbering scheme is set up.

Of course, if the balance of the document is already printed, and the new pages are in a separate document, on those pages you could just use

###-{ PAGE \* ALPHABETIC }

where ### is the number of the page following which the new pages are to be inserted.