It appears that the phase “ScScS” (i.e., not ScSScS or ScS2) is a valid phase for phase_list. This is also the case for Philip Crotwell’s TauP codes. The taup_time output for:
prompt> taup_time -mod ak135 -ph ScS,ScScS,ScSScS -h 0 -deg 0
Model: ak135
Distance Depth Phase Travel Ray Param Takeoff Incident Purist Purist
(deg) (km) Name Time (s) p (s/deg) (deg) (deg) Distance Name
0.00 0.0 ScS 935.77 0.000 0.00 0.00 0.00 = ScS
0.00 0.0 ScScS 1265.67 0.000 0.00 0.00 0.00 = ScScS
0.00 0.0 ScSScS 1871.54 0.000 0.00 0.00 0.00 = ScSScS