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...I forget exactly which was which, but the essential differences in geometry that unfolded over the Merckx steel bike lineup were between the slightly steeper full race geometries, and those with slightly more relaxed angles and longer to tubes that were labeled Century.
I'm not 100% sure if there is much difference between a Corsa and a Professional, geometry wise. I have a couple in the garage, and I still don't really understand any differences in hierarchy other than that Century line being designed for longer distance riding so that you don't get beat up by the bike.