Howdy,
I think there's every reason to expect that your old steel had the toe and heel ground off, so that you were no longer on a standard 10' profile, given what you've described.
Pop the blades out of each, overlay them, and look? If they're both still 10' radius, they should line up. That's not going to tell you anything about pitch differences (since that involves the holder), but it would at least tell you if your old blades had essentially been re-profiled to something like a multiple radius by sharpeners taking off the toe and/or heel.
Mark
(who is very much not an expert, so you get what you pay for here. 🙂