The replacement images were fine.
I sent in a small order of 3-5 x 7s in sepia and 1-8 x 10 in B&W to test the soft proofing. All of the prints turned out perfect. This will be my method going forward. That way, if I get something too dark, I'll know it's them.
I also recalibrated the monitor just to be sure. Only minor adjustments, I supposed they may have had some impact as well, but probably not as much as the soft proofing.