There are two issues with your mailmerge:
1. Whatever the process is, it uses an addin that employs non-standard fields. The TableStart:LineItem and TableEnd:LineItem codes evidences that. Consequently, what you can do may be limited by what your software supports - unless, of course, you can access the database via a standard Word mailmerge.
2. Assuming you have the required flexibility, the next issue is: How would the mailmerge process identify which records to combine? Indeed, are they different records, or are they perhaps different fields from the same record?

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]