They clearly didn't forget that The Sing-Off gave them their start. The group helped a petition to bring the show back and guest starred when the show was revived for a fourth season. They also appeared on the 2-hour special that aired in December 2014 in lieu of a fifth season.
During their time on The Sing Off, when they were trying to arrange their cover of "OMG." Kevin admits that he's having a hard time connecting to the song because the more explicit lyrics conflict with his religious beliefs. Rather than giving him a hard time, the group meets him halfway and changes the lyrics, with Scott saying that the performance isn't going to be any good unless everyone is feeling it. What's really impressive here is that most of their cleaned up covers function almost as well as the original— which is extremely hard to do in a song like "OMG" or "Thrift Shop," where the explicit lyrics are often the "hook," or the most catchy and memorable parts of the song. Most attempts to clean up music like this tend to be very intrusive, because everyone knows exactly what's being changed. Pentatonix was willing to find a workaround and sell it, for Kevin's sake.
The group released seven different videos for their original song "Can't Sleep Love"—one with all five of them, one with all five of them and Tink, and then five videos that star each individual member of the group and no one else (well, Avi and Kevin cameo in each other's videos, but only for a few quick shots). It's like the group is trying to show everyone that each member of the group is equally important, and that all five of them make up Pentatonix, not just a couple of them while the rest back them up.