My guess is that whatever print they had for the mag audio was too physically compromised to pull a stable sound capture. I can tell you from personal experience that Fantasia’s a tough find in good condition w/ the mag stereo mix; more than half the time, the colors turned almost entirely to red, the print has vinegar syndrome, and/or each reel has warped to some degree. The funny thing is that Thunderbean’s release does use the mag mix for the interstitial segments, but that’s it, and those portions also spread the LCR channels across the six-channel field.