Sometimes they skip numbers for the train stations, to prepare
for future stations in between long distance stations.
Some examples:
Kranji(NS7)---Yew Tee(NS5)
Yishun(NS13)---Sembwang(NS11)
Harbourfront(NE1)---Outram Park(NE3)
Well, these are all i know that skip numbers. Hope u have a clearer
idea now.
