MT,

I have Version 2015 (417)

I have:

M_RBRKRL.STY. RB RocknRoll w MST Piano[165MST]
Real and MIDI SuperTracks. Quartet.
RD: ROCKNROLL^02-a: Swinging Ride, b: Two Beat Cymbal :
RT2351: Bass, Acoustic, RockabillyRockNRoll Ev 165 , Dave Roe

** N/A ** MIDI ST2472: Piano, Rhythm RockabillyRockNRollKevin Ev 165 , Kevin McKendree

RT2352: Guitar, Electric, Rhythm RockabillyRockNRollBrent Ev 165 , Brent Mason

But the piano shows it is not available. The other instruments are there.