Over the years Watkins and Thomas have been accused of marginalizing Lopes’ legacy -- especially after a 2005 UPN reality show competition, “R U the Girl,” offered a prize to record and perform a track with them. And rumors that Lil Mama, who performed Lopes’ raps alongside TLC at recent gigs, would become a permanent fixture have incited fans.

The two say they are not -- and never were -- interested in finding a replacement for Lopes. It’s the one topic that gets them the most visibly upset in conversation.

“It's almost offensive,” Watkins said, along with a few unprintable words. “We built this together and we are always gonna have this together. It seems like no matter how much you're saying it, you're still always explaining yourself.”

Whether TLC finds a new generation of fans remains to be seen, but its comeback campaign is forging ahead. Gail Mitchell, a senior writer at Billboard, believes it will stick. “There's enough love and legacy of the time they were together that they can do this,” she said. “A next generation of R&B seems to be tapping into the '90s R&B, which is when TLC was big, so this might be perfect timing.”

Back at the recording studio, Watkins is discussing the new material and what could work as a potential first single. She was partial to a particular track, but a producer was lobbying for another that could hit multiple radio formats. “We had to beg L.A. [Reid] to do a video for ‘Waterfalls,’” she argues. “That was our version of going alternative.”

After another check on Thomas, Watkins slid into a dimly lit booth to take a stab at another song -- an angsty, guitar-driven pop-rock ballad called “Breaking Bad.” 

“If I die before I wake, at least I know I lived for something,” she sang. “If this breath is the last I take, I don’t want it to be for nothing.”

“We’re back on the train now, and just going,” Thomas said. “This movie has opened so many doors for us. We have a new record deal. We’re back with L.A. Reid. It’s amazing how everything is falling into place. We’re just ready for the ride.”