Can WP Smush Pro compress previously uploaded NextGen jpegs?

One of my site’s WP backup export procedures (All-in-one Migration) no longer works because my site’s image files are too huge, so I looked for a way to drastically reduce the storage requirements of my preloaded bloated image files so that my AIO Migration export would work once again.

I installed WP Smush Pro onto that WP site that uses NextGen Gallery for displaying user photos. Some of the photos that had been previously uploaded for NextGen are .jpg files that are huge (6-7 mb) and I was hoping I could run Bulk Smush and it would go thru them all and drastically reduce them in size. To do this I installed Smush Pro, configured it to allow max image files to be no more than 1024 x 1024, configured it to work with NexGen, and then I ran the Bulk Smush buy the NextGen images remained unchanged from their original huge sizes.

A typical directory containing these previously uploaded files is /wp-content/gallery/2012 in case that is useful.

Perhaps I misunderstand how Smush Pro works with NextGen. Can I not do a Bulk Smush to reduce my overall file size for even NextGen gallery images?