Bill, thank you for the very quick reply. I just posted another question about creating galleries and I believe the answer to both questions is the same: I must upload images to the page, regardless of whether or not the same images exist in my Media Library.
You’re using the post_parent field to pull the images for both the “Individual Portfolio” page template and the Gallery, and there can be only one post_parent. Got it!
Instead of uploading my images to the gallery in advance of building the pages, I’ll need to upload on a page by page, or post by post basis.
Thanks,
Michael