Richard - this is immensely helpful for sure. I looked at the wrong htaccess earlier today. Here is a section from the correct .htaccess that I think identifies with what you are referring to:
From Ultimate SEO URLs
RewriteRule ^(.)-p-(.).html$ index.php?main_page=product_info&products_id=$2&%{QUERY_STRING} [L]
RewriteRule ^(.)-c-(.).html$ index.php?main_page=index&cPath=$2&%{QUERY_STRING} [L]
RewriteRule ^(.)-m-([0-9]+).html$ index.php?main_page=index&manufacturers_id=$2&%{QUERY_STRING} [L]
RewriteRule ^(.)-pi-([0-9]+).html$ index.php?main_page=popup_image&pID=$2&%{QUERY_STRING} [L]
RewriteRule ^(.)-pr-([0-9]+).html$ index.php?main_page=product_reviews&products_id=$2&%{QUERY_STRING} [L]
RewriteRule ^(.)-pri-([0-9]+).html$ index.php?main_page=product_reviews_info&products_id=$2&%{QUERY_STRING} [L]
You are correct - there is a plug-in in the old ZenCart site that created the "seo friendly URLs". I think it created a database table to matrix the Zen Cart internal page ID's against it's calculated SEO friendly URLS (that's what this redirect looks like to me - see above.
Do you think all is lost because of the amount of time that it's been since the migration, or do you think if I can mine the original database and recreate the ID -> Old URL mapping as new 301 redirects, I might recover this? Makes me sick to my stomach to think that we lost reputation from pre-2008!
Thank you for the continued conversation!