Service 852 had these replacements due to the fact that KJDEP
transferred duties to AMDEP.
For those ex CSS CAC Nissan UDs, I remembered that WLDEP initially
had TIB1248D-TIB1250X whereas AMDEP got TIB1251T-TIB1256E. A lot of
such Nissans made appearances on services 167, 171, 852, 853, 855,
961 followed by 980. More of them got transferred over to WLDEP and
made cameo appearances on Bt Panjang feeders 920 and 921. Service
980 under WLDEP also had permers for a short while if I am not
wrong. After Feb 2006 Bt Panjang feeders got back their former Merc
perms, and eventually landed on perm service 178 
TIB1257C was once former CSS310U and was perm service 608. After
becoming TIB registered, it did cameos on AMDEP services like
services 67, 171 etc. Eventually became service 980 permer in June
2005.