After a split casts doubt on the future of the titular band in the 1984 mockumentary This Is Spinal Tap, lead singer David St. Hubbins (Michael McKean) tries to put the band's tangled history in perspective. "You saw exactly how many people have been in this band over the years," he says to the camera. "Thirty seven people have been in this band over the years."

Fifty years after its formation, Deep Purple has invited less than half that number into its ranks. Still, its family tree can get a bit convoluted – leading to situations like this weekend, where Philly-area fans have two opportunities to hear the band's music live. This Sunday, the latest incarnation of Deep Purple (Mark VIII, according to fans' accounting system) will co-headline Camden's BB&T Pavilion with Judas Priest – which has replaced its own share of members over the years, most famously setting the precedent of hiring a tribute band singer to step in for vocalist Rob Halford and inadvertently inspiring the otherwise uninspired Mark Wahlberg vehicle Rock Star.

Two days earlier, Mark III and IV vocalist Glenn Hughes (who shared front man duties from 1973 to 1976 with future Whitesnake founder David Coverdale) will belt out his own versions of the band's classics under the title "Classic Deep Purple Live Performed by Glenn Hughes."

Hughes says the intention is not to market himself as another version of Deep Purple – one of many bands he's fronted, a list that also includes Black Sabbath, Trapeze, and Black Country Communion – but to revive songs that the current lineup has left on the shelf. "I decided that during the time I have left to sing in my life, I needed to look at the legacy of the material I wrote in the '70s. The current Deep Purple do not play these songs, so while I'm in such fine fettle – spiritually, mentally and physically – I thought it would be a good time."

As long as there have been rock bands, there have been ego clashes, fractures, and replacements. What seems to be new these days is a kind of musical mitosis – bands splitting into multiple parallel versions, crisscrossing paths as they tour the country to play for increasingly confused fans.

"It's weird for us to have to compete with ourselves," says Jay Aston, front man and cofounder of '80s goth-pop band Gene Loves Jezebel. In one of the strangest twists on the trend, two versions of the band currently exist – each led by a separate, feuding twin brother. Jay Aston's Gene Loves Jezebel – as they're legally obligated to refer to themselves in the States – will play Kung Fu Necktie on Saturday as part of their first North American tour in a decade.

Later this month, brother Michael Aston's version of the band – which has to use his name in the UK, but simply goes by Gene Loves Jezebel on this side of the pond – will play the Electric Factory on Sept. 29 as part of the Lost '80s Live tour, alongside A Flock of Seagulls and Wang Chung, among others. The two takes on the band stand in stark contrast: Jay's version, with members that have been in the band for 30 years, supporting their strong new album Dance Underwater, while Michael and his supporting band thriving on nostalgia for old hits like "Desire" and "The Motion of Love."

"Legally we're not supposed to say anything negative," Jay says. "But they're our songs and the band that I'm in is the band that's been touring since 1985. That's the band that everyone knows. I personally can't imagine ever going out and singing someone else's songs every night."

A similar situation exists for other warring bands. As of last year there are now two versions of Yes: one led by longtime guitarist Steve Howe, the other called Yes featuring ARW, with founding singer Jon Anderson, guitarist Trevor Rabin and keyboardist Rick Wakeman. There were two Queensryches and two L.A. Gunses for a time, until the former settled their differences in court and the latter reunited.

Fellow '80s hard rockers Great White continue a dual existence: one, the original band that now includes founding guitarist Mark Kendall and other long-standing members, and Jack Russell's Great White, led by the classic-era vocalist known for "Once Bitten, Twice Shy" and supported by a band of hired guns. "I don't call ourselves a version, because we've always been here," says Kendall. "We changed singers, but it's not like I look around and don't recognize anybody in my band."

Great White's lineage just got a bit more complicated, with the announcement of new singer Mitch Malloy – who was tapped by Van Halen to replace Sammy Hagar in 1996 but only lasted for a few weeks before the relationship fell apart. He's joining Kendall's version.

"We'd love it if every band had all their original members," Kendall laments, "but sometimes it's just not possible. Things happen that are out of your control. We've played with bands where just the drummer is the original guy, which is pretty extreme. But sometimes the music becomes bigger than the band."

HEAR THIS

Classic Deep Purple Performed by Glenn Hughes

Jay Aston's Gene Loves Jezebel

Deep Purple/Judas Priest