Any idea what the stampings on the INSIDE of the rear dropouts means? I have a Super Corsa (date stamp 4431, so 1971) with a large "L" above "0" inside both rear dropouts, and a Tour de France (date stamp 3272, so 1972) with "Y" above "2" on the inside of the dropouts. I also have a 1971 Tour de France (date stamp 1231) which does not have any marking on the insides of the dropouts.