I've heard this statement before. Unless you have the "master tape" at your disposal as well as the machine it was recorded on, speakers that were used for monitoring / mixing, etc., one has no clue as to what it sounds like in its "original" form.
I largely agree, except the tape is what it is; I don’t think we need the studio’s junky monitors to know that the tape can sound better on a good high-end system.
It is a figurative or a mainly theoretical concept, unless one has the safety copy of the master.