Yes, that looks like a Columbus SL decal, so it should be a C80. It's 1978-1987 based on the Columbus decal style, so it may be 1984, per the derailleur patent date. There should also be component dates on the back of the crankarms and hubs' locknuts. If they all match, that should increase your confidence in the date. This Bertin decal style has also been seen on models with Shimano Dura-Ace AX, which were 1981-1985, so that fits too. Hopefully, Jim will be along shortly to provide a more informed answer.