Yes. Same with the front valances. To my knowledge, the later (black) service parts were not galvanized. Reproduction parts were never galvanized either (to my knowledge). I have found every one of the three red oxide OE Ford service replacements I have used as galvanized so far too. I suppose it wouldn't be safe to say EVERY red oxide service replacement is galvanized but it seems to be a determining factor.
During the first attempt to do a quicky restore on my SJ car I replaced the front fenders and rear valance with black Ford service replacements. We body worked the pieces and the car was nearing final block. Then we moved and things went really stale with this specific project. Kind of like "Garage Squad."
Anyway, I rethought all of the replacement metal. I repaired some small rust holes in the original fenders, then stripped and hammer/dollied the original valance.
As you guys stated, the original is galvanized and the black Ford replacement was not.
