Here's what is in the Scott catalogue. Hopefully you can match the dates with the SG.
Top row, left to right....
Travancore 1946 8ca rose red (Scott 48)
Travancore-Cochin (Official stamp)1949 1/2a on 1ch yellow green (Scott O3)
Tranvancore-Cochin 1949 1a on 2ch orange (Scott 4)
Travancore-Cochin (Official stamp) 1949 2p on 6ca violet black with red overprint (Scott O1)
Travancore-Cochin 1949 2a on 4ch henna brown (Scott 5)
Four of the five stamps are actually from the combined state of Travancore-Cochin.
Scott shows the "service" overprint, and refers to the previous type "a' overprint, so nowhere do they show the actual full overprint for the Official stamps. If SG does the same thing, it will easily lead to confusion unless careful reading is done.
Hope this helps.