Well, the OP suggests in the Subject "LP nobody ever heard of".
And yet some mention albums by Sonny Rollins, Jefferson Starship, Captain Beefheart, T Rex, John Mayall, etc. I expect if those specific LPs were not big sellers they are at least known to come extent.
So, many may know Ricky Nelson but how many have heard his last album, "Memphis Sessions"? Then there is "Jazz at Toad Hall" by Ken Moule, anyone know that one?