While I was looking at a Peugeot Tandem for sale on craigslist, I noticed a dusty De Rosa in the man's garage. I inquired and it was offered to me for $200 firm. Despite being the original owner, he didn't remember the model or exact year (1989-1991ish), but he did inform me that it had been repainted.
It had Campy Record Hubs with tubular tires, Campy Athena bottom bracket, Campy Chorus index shifting with 9-speed cassette, and clipless Look pedals with shoes in my size (while not necessarily valuable, it would give me a chance to try clipless).
It also had all the De Rosa pantographing I would expect (fork crown, seat stay, and dropouts [which also had adjuster screws]) At 62cm, it fit and rode quite well. Were the bike in perfect condition, obviously there would be no question in my mind.
However, there was a small to decent amount of rust, and I do not know how much rust is too much. The bottom bracket shell was pretty externally rusty, but there were also two dime sized patches on the top tube. It looked as if rust had been painted over, then bubbled up, breaking the paint (if that happens). It seemed sturdy, but it got me too spooked to make a decision.
As I was unable to take pictures, you will have to use your imagination.
Thanks so much!