Robert Johnson's records mastered at wrong speed?




http://www.guardian.co.uk/music/musicblog/2010/may/27/robert-johnson-blues

Experts say Robert Johnson's classic blues records all mastered at wrong speed - took 50 years to figure it out.... Anyone glad to hear he's not really a chipmunk?
gdoodle
JazzCourier your experiences sound truly amazing; what a fortunate circumstance in which to be involved. Thanks much for sharing
Somebody needs to run this by Honeyboy Edwards. I believe he is one one of the last people around who played with Johnson. Talk about acoustic memory, this would be a new record.
While I certainly think it is possible that they are at the wrong speed, 20% seems like a rather high number.