NASHVILLE, Tenn. – Even if you only occasionally listen to radio, you’ve probably heard Carrie Underwood’s revenge anthem “Before He Cheats” … and heard it, and heard it, and heard it.

The tune is on Underwood’s 2005 debut album, “Some Hearts,” and it first hit the charts back in February 2006. So why now, two years later, is “Before He Cheats” up for song of the year at the Grammy Awards on Sunday?

Because the Grammy rules allow it.

Indeed, Underwood’s megahit isn’t the only song of the year nominee that could, at least to fans, feel stale. “Hey There Delilah” by the Plain White T’s was on the group’s 2005 album, “All That We Needed,” though it didn’t become a hit until two years later. “Like a Star” by Corinne Bailey Rae was released as a single in 2005 then rereleased the following year.

For most nominees, the music must be released in the eligibility year, which in this case is Oct. 1, 2006, through Sept. 30, 2007. But there are exceptions, and two of them are song of the year (awarded to the songwriter) and record of the year (awarded to the performer and production team).

In those categories, a single is still eligible if it was released in the preceding eligibility year but “achieved prominence” in the current one.

“A record is not like a movie,” explained Greg Bechtloff, a project manager for the National Academy of Recording Arts and Sciences, which presents the awards. “A movie comes out and it’s out. It either sinks or swims. But a record can grow.”

Even so, the rules have made for some interesting Grammy moments, like in 2006 when Billy Joe Armstrong of Green Day, while accepting record of the year for “Boulevard of Broken Dreams,” mused that it had come out “something like two years ago.”

The win also seemed a case of deja vu because only the year before Green Day had won best rock album for “American Idiot,” which included “Boulevard of Broken Dreams.”

“It confused a lot of people and made us look weird,” Bechtloff said.

Ditto for U2. The band cleaned up with their album “How to Dismantle an Atomic Bomb,” including best rock song for “City of Blinding Lights” and best rock performance for “Sometimes You Can’t Make it on Your Own,” in 2006. But they won the same two categories in 2005 for “Vertigo” from the same album.

This year, Beyonce Knowles could have her own Green Day moment. While her album “B’Day” won best contemporary R&B; album last year, she’s nominated for record of the year for the single “Irreplaceable,” which, coincidentally, peaked back in December 2006.

All of this is bound to puzzle some Grammy viewers.

Garth Fundis, a member of the academy’s board and a former chairman, said the board has discussed trying to “shorten the window” to freshen things up, perhaps by moving the show closer to the end of the eligibility period, in October instead of February.

“But there’s no way to do it. There’s always going to be that lag time,” Fundis said. “Getting the information out to the members and letting them vote and get the final nominees and then vote again – it takes time to do all of that.”

The process also is hindered by the slow movement of singles into radio rotation, particularly on the country side.

“For fans of the artist, it may seem that a song as part of the album has been around forever” even though as a single it meets Grammy eligibility, said Silvio Pietroluongo, director of Billboard magazine’s genre-spanning Hot 100.

Underwood’s “Before He Cheats” debuted on the country charts in early 2006 before Arista Records even began promoting it. After the label pushed it as a single, it climbed to No. 1 in November of that year and stayed five weeks.

The song crossed over to pop stations in 2007 and reached No. 9 on Billboard’s Top 40 chart in May. It had yet another run on adult contemporary, peaking at No. 6 in September.

In all, the dark tale about a jilted lover vandalizing her boyfriend’s truck spent a remarkable 64 straight weeks on the Hot 100.

And thanks to the Grammys, it’s not going away quietly.