Yeah, what he said.

50s and 60s, Gran Sport chrome rear derailler with the box front... early 60s they added the Record rear which looks the same as a Gran Sport but says Record and the Record front derailler, which looks like a Nouvo Record but with a cable stop built in the body.

Nuovo Record was an alloy bodied rear, came out late 60s, Super Record, early-mid 70s had a revised cage and some black parts, but they are functionally similar. So is the Nuovo Gran Sport by the way, a cheapened version of the NR.

Avoid the Valentinos, Veloxes and variants, a cheap stamped steel rear designed to bring Campagnolo to the masses that made Huret look highly functional.