Depends on what you're measuring. The lowest THD number I have seen for a vinyl record was 1%. Also, calling a Pink Floyd or any other vinyl album "already perfectly mastered" is either being unaware or ignorant of the fact that a perfect master is on the master tape, not the album. Mastering for vinyl means that the mix and EQ needs to be adjusted for where the song lies on the record. At the outer areas, the highs and bass can be more neutral but near the label, the EQ must be different because the there's more inches/second of vinyl passing the needle at the outer part and less inches/second at the inner part of the groove. It's constant angular velocity but not constant linear velocity. If you listen to some of the first CDs, listen to how different the EQ is when you compare what would be the first and last songs of each side of the original album.