Looping in Word mail merges/ checking for missing fields

Question

I am trying to convert a project that uses WordPerfect merges to use Word mail merges.  One issue that I am encountering is that I cannot find a way to use any looping structures in Word mail merges. Specifically, my data file is a csv text file. 
I control the contents of the file but its current structure is that it will consist of a single record (not counting the header row).  The number of fields will vary but it will contain a field named Person1.  There may or may not be a field named
Person2, Person3 etc.  There are several of these types of fields in the record so it is not an option to make a separate record for each person ie for the record I will have Plaintiff1, Plaintiff2... and Defendant1, Defendant2....
I am having trouble with two things:
1. how can I test for a blank or missing field ie I want to have a statement like {if {MERGEFIELD Defendant2}="" "Defendant is" "Defendants are"}.  That statement works but it throws error messages to the user that the
field Defendant2 is missing and prompts them to substitute another field.  That sort of statement occurs multiple times during a merge so asking the users to ignore the errors is not an option.
2. is there some sort of looping mechanism in Word mail merges.  I need to be able to do two things with a loop:
a.  I need to be able to list each of the Persons, Defendants, Plaintiffs ie. While {MERGEFIELD Defendant{#}<> "" " {MergeFIELD Defendant{#}" (increment variable # by 1).
b.  I some circumstances I need to create full documents based on a loop i.e.  While {MERGEFIELD Defendant{#}<> "" <<merge a defendant summons here>>(increment variable # by 1)

Answer 1

For clarification: In a Word mailmerge, if any of the field headers are missing from the data source, you will get an error. Thus, you can't have a mailmerge main document that references «Plaintiff2» or «Defendant2» and not have the corresponding headers
in the data source. The fields may be empty, but the headers must exist.
Re 1:
You can indeed use an IF test along the lines of:
{IF«Defendant2»= "" "Defendant is" "Defendants are"}
or:
{IF{MERGEFIELD Defendant2}= "" "Defendant is" "Defendants are"}
Re 2a:
Creating a list is as simple as inserting the mergefields one after the other:
«Defendant1»
«Defendant2»
«Defendant3»
This will, of course, result in empty lines when fields have no data. To cater for this, Word provides the mergefield \b and \f switches.Given you can have one or more defendants, you could suppress the extra lines via, say, an \b switch:
1. select the
«Defendant2» field and press Shift-F9 so that you get {MERGEFIELD Defendant2};
2. edit the field code so that you get {MERGEFIELD Defendant2 \b "¶
3. delete the paragraph break or line break after the field, so you get:
«Defendant1»
{MERGEFIELD Defendant2 \b "¶
"}«Defendant3»
where ¶ is a real paragraph/line break
4. Do the same for the «Defendant3» field and so on, till all are done.
The following construction can be used to manage data where one or more related fields («Defendant2», «Defendant3», «Defendant4», «Defendant5», & «Defendant6») may or may not be populated, so you can get commas before all except the last in a multi-defendant
sequence, which is preceded by 'and'.
«Defendant1»{IF«Defendant3»= "" " and «Defendant2»" ", «Defendant2»{IF«Defendant4»= "" " and «Defendant3»" ", «Defendant3»{IF«Defendant5»= "" " and «Defendant4»" ", «Defendant4»{IF«Defendant6»= "" " and «Defendant5»" ", «Defendant5» and «Defendant6»"}"}"}"}
Note: It is assumed that none of the fields after the first empty one will be populated.
Re 2b:
It's not clear what you're after here. However, in addition to using an IF field as per 1, above, they can also be used to conditionally output multiple pages, including text, tables and images, together with additional mergefeilds on those pages. For example:
{IF«Defendant2»= "" "«Defendant2» is a nasty fellow ... plus the rest of defendant 2's content & mergefields"}
Note: The field brace pairs (i.e. '{ }') for the above examples are created in the document itself, via Ctrl-F9 (Cmd-F9 on a Mac); you can't simply type them or copy & paste them from this message. Nor is it practicable to add them via
any of the standard Word dialogues. Likewise, you can't type or copy & paste the chevrons (i.e. '« »') - they're part of the actual mergefields, which you can insert from the mailmerge toolbar. The spaces represented in the field construction are all required.
Instead of the ¶, you should use real line/paragraph breaks.
For more Word mailmerge tips, see:
http://www.msofficeforums.com/mail-merge/21803-mailmerge-tips-tricks.html . That page also includes a macro for turning the above field representations into working field codes.
Cheers
Paul Edstein
[MS MVP - Word]