The absolute answer (2001-2017) .... is there a box behind the rear wheel that you have to remove the seat and unplug to be able to roll the rear wheel out the back (not using the "beached whale" tire change method nor a lift)? That box is the amplifier of the Premium Audio. I also agree that all "1" vin bikes for US sale will have Premium Audio.
MORE level info:grin2::
2001-2005: ABS or Non-ABS
Early 2006:
Level 1: Premium Audio
Level 2: Add Comfort Package
Level 3: Add Navigation
Level 4: Add ABS
Late 2006-2008:
Level 1: Premium Audio
Level 2: Add Comfort Package, Navigation
Level 3: Add ABS
Level 4: Add Airbag
2009-2010:
Level 1: Premium Audio, TPMS
Level 2: Add Comfort Package, Navigation/Weather/XM
Level 3: Add ABS
Level 4: Add Airbag
2012-2017:
Level 1: Premium Audio, TPMS, Comfort Package
Level 2: Add Navigation/Weather/XM/Trip Planner
Level 3: Add ABS
Level 4: Add Airbag