I'd say that frame was made after '86 due to the "DeRosa," and Ugo's signature, on the top tube, and the fully chromed fork. The graphics and color look like it definitely could be from the '90s.I got into the sport in the mid to late 80's. I had the Gita catalogues of that period & may still have some around somewhere. All of the De Rosa offerings from 86 on up all offered flat fork crowns. That was the most notable feature of those bikes.
Mine was made in '84 or '85. It's SL with an SLX seat tube, a possibly romantic flourish a year or two ahead of its time. It has a chromed flat fork crown, painted fork, chromed drive side chain stay, and no bridge.
I think flat fork crowns have been around since the '20s. A book on frame builders I lent to a bike club member [He never gave it back], said that Chino Cinelli pioneered a "fully sloping" fork crown in the '70s, claiming it tightened up the front end in all directions. Flat crowns were nice and stiff laterally, but some cool guys found them too flexy fore-aft, the whole point of flat fork crowns!
Nice frame in pristine condition! Have a nice build!