Hi John,
Thanks for your reply. Yes, I did actually get this worked out. And no, neither use of the images was via short code. The gallery images are being used for an XML feed (no watermark), while the basic attached images are displayed on a single post page via a custom loop (with watermark).
I figured out that all I needed to do was loop through my gallery images, then exclude them from my main attachments loop. Voilà!
Cheers,
-jennyb
