It seems to me that in 1994, they had cleared the theme (perhaps because they got the theme free and clear with the Barris program library), but Barris wouldn't clear the interior cues (he didn't write the win cue, so that got cleared). So they brought in Steve Kaplan or someone like him to write soundalikes they could layer over the original cues. By 1998 and the appearance of "3s a Crowd" on the GSN schedule, it was obvious that the clearance issue had been resolved (most Barris 70s shows use the same cues, the two fee plug cues especially), but they didn't bother going back and remastering "TNG."
IIRC, what kept and keeps 70s "TH" off of GSN are two Crusaders songs, one of them their minor hit "Put It Where You Want It." They were both used as bumper cues coming out of the segments where the contestants have picked their boxes, Geoff holds up the cash envelope and says that he'll open it after the break.