Why not take a master tape reel to reel, played back on a well set up Studer machine (or any other decent tape player) and compare it to all the arms and cartridges combinations you think are 'right'. The one closest in performance to the master tape 'actual' recording is clearly more true and will do so on all other LP's. Hearing more out of the LP recording (piano more fuller and sustained note or more texture on strings) is then not a true sign and clearly shows that information is getting added on. This was not there in the first place on the recording.
Not many will have the capability of getting a RTR comparison, but having a good digital transfer in DSD or DXD playback could be another option for comparison.