Unfortunately this is not the case. You listened to tapes that were slowly deteriorating over time played on a tape deck that added it's own colorations played through speakers or headphones that also added colorations.
This is not exactly true- the tapes were new, the tape machine was rebuilt and very stable and calibrated. This is the sort of thing that you apparently have to do in order to understand how powerful it is as a reference! I've seen audiophiles turn ghost white after being fooled by the direct microphone feed (startled at how *real* it sounds- far more so than any stereo using a recording can!).
The value of working with master tapes is that you are there at the recording session so you *know* what the music is supposed to sound like.