I went to the National Library today to do some research, having found bus guides dating back to 1980 but no time previously (

) . I took the 1980/1981 SBS Bus Guide and compared a few routes with the ones listed in the 2006 Transitlink Guide (routes 169, 170, 284, the A.M.K. feeders, and the Bukit Merah feeders). What I found (if I remember correctly) was this:
• route 169 used a slightly different route inside Ang Mo Kio, and it's route from Sembawang Road onwards follows the current route 856 almost exactly (except it didn't go into Senoko), right up to the old Woodlands interchange (the current Woodlands Interchange didn't exist back then, as we all know)
• route 170 has no change for the Singapore portion since 1980, but clearly uses a different route in Malaysia.
• the 1980/1981 Ang Mo Kio feeder routes are barely recognisable today when compared to their current routes
• now, this is amazing: for routes 272, 273, 274, and 284, there has been virtually
no change in their routes since something like
26 years ago! Also, at that time, route 275 didn't exist (it was probably introduced sometime between 1982 and 1986, drawing from the different old bus guides I found there (the 1982 and 1986 editions were the ones I found and used)), and even then, that route has no change since then! However, there is this one withdrawn route 271, which used to loop at Telok Blangah Crescent. One thing that I did took notice of, and which I jotted down notes of, is this route 270. Footnotes say that this route will only be implemented as a "Ring Service" under some "Telok Blangah New Bus Plan". Plotting the route on a map, I could see that it looped at two places (specifically, Telok Blangah (T.B.) Street 32 and T.B. Rise, with the former first), in a fashion faintly similar to how intra-town (Townlink) buses loop at two places in a new town. The "return route" simply meant that the bus could go to T.B. Rise first. The weird thing was, this route completely ignored the bus interchange, and terminates inside a J.T.C. Factory. Also, there was no mention of this route in the 1982 bus guide; it seemingly was never introduced in the real world, only listed. Either that, or it got withdrawn very quickly after it's introduction. What gives?