Let's list out the buses which have perm on the same service on more than 1 occasion:
SBS9155D 157 - (1996-2001, 2009-2011)
SBS9254B 99 - (1994-200?, 200?-2011)
SBS9259M 99 - (1994-199?, 200?-2011)
SBS2732J 123 - (2008-2010, 2012- current)
SBS5130B 95 -(2010-2011, 2012)
SBS5130B 123 - (2011-2012, 2012-current)
SBS1688K
Former Service 84(Punggol-Punggol Drive)
Current Service 84 (Punggol-Punggol Rd END)
SBS9199C 72 (199x - 2002/03, 2012 - current)
Almost forget about this one:
SBS2596K -195 (1996-2000, 2012-)
I rmb 9314L and 9522C was perm 168 then SP then return to 168 again
TIB661A on 160/980 (1998-1999, 2010-dereg)
TIB664S on 980 (1999-2000, 2010-dereg)
TIB665P on 160/980 (1996-2000, 2001-dereg)
TIB666L on 980 (1998-2000, 2001-2004, 2010-dereg)
TIB782J on 160/980 (Jan-Jun 1998, Jun 2000-Jan 2001)
TIB503Z on 167 (1995-1998, Jan-Mar 2001)
TIB503Z on 980 (2000-Jan 2001, Mar 2001-2003)
TIB504X on 167 (1995-1996, 2001-2003)
TIB502B on 858 (?-2011, 2012-current)
TIB425R TIB426M
WLDEP 61 > WLDEP 75 > KJDEP/AMDEP 61
6079K
AMDEP SP to BRBP 131 to BRBP SP to AMDEP SP to AMDEP 24 to BRBP 131