I carefully edited email addresses in a separate Outlook Contacts folder to
make sure each contact had ONE and ONLY ONE email address.  I then selected
that folder in the Word mail merge process.  Resulting emails went to
addresses I had deleted from the selected Contacts folder, although most
existed in my main Contacts in the email-2 field.  YES, I'm sure I selected
the correct folder.

Perhaps this occurred because I did the initial select to write the letter,
THEN made changes to the Contacts folder, THEN closed the Word Document and
reopened it (which asked me to select the Contacts folder I wished to use).  
It looked like it should have worked, but maybe it had already selected and
held the data?

If this is the case, instructions somewhere should include editing addresses
as a preliminary step for mail merge.