The only place I've heard say there is a Roma Red Si is Honda. It's only listed for 1999.
I'm sure there could be some out there that go undetected. I mean, most people think Eran's hatch is the same color as my coupe. I've seen multiple peopel who own hatches think that they're Milano Red, but then they check, and come to find out, the code is R-97.
I woulcn't be surprised that most people, when wondering their car's color, just read down the list and say, "Oh, that sounds like my color." It's probably more likely for Si owners because it's well spread that the Si only came in three very different colors. It's not like you're going to confuse Elctron Blue Pearl and Flamenco Black Pearl. But Milano Red and Roma Red are often confused. The biggest difference is the Roma is a little more orange, the Milano a little more pink, and the Milano has a tricoat. It can be difficult to tell in photos though (unless the cars are next to each other).
The only thing I'm confused about is that I've never seen that Roma Red was painted at the US coupe plant.