Can I ask for another vague hint? Were all four titles originally issued by labels that fell under the WEA umbrella? Jefferson Starship was a surprise as it had been reissued through Sony/Legacy on CD as recently as 2005, but my guess is that Jefferson Starship retained the masters once they started Grunt in 1971, at least that sounds plauseable. I imagine Chicago also secured their masters from Sony somewhere down the line. But is Rhino licensing titles from other majors? If so, please do what you can to get Marvin Gaye's "What's Going On" out in quad.
Just to put my 2cents in, I'd love to see these ones come soon (all were originally released on CD-4 LP, quad reel & Q8 tape)...
Mickey Newbury • Frisco Mabel Joy
Donny Hathaway - Extension Of A Man
Herbie Mann – Hold On, I'm Comin' (for me better than Push Push and with a nice discrete mix)
Jackson Browne - Late For The Sky