MOST WEB USERS WHO HAVE streamed prime-time shows on NBC.com did so after missing the episode on its original air date, but a large proportion also went online to watch a show a second time. Those are among the findings of a report issued Wednesday by NBC Universal. Seventy-eight percent of the users of NBC Rewind–the network’s full-length online video player–said they have streamed a program because they missed it when originally broadcast. But 26% said they have streamed an episode they already saw on the air, and 34% have watched a program they had never seen before. Starting last October, NBC made full episodes of “Heroes,” “30 Rock,” “Friday Night Lights,” “Las Vegas,” “Studio 60” and “My Name Is Earl” available on NBC.com for streaming. Joining the roster this year are “Grease: You’re The One That I Want” and “The Apprentice.” NBC also reported that more than 60% of users stream full episodes on the site. To date, 6.9 million users have streamed almost 42 million videos on the site, according to NBC. For the report, research company Insight Express surveyed 1,520 visitors to the site between Nov. 14 and Dec. 18.