Just something on what I observed over the years..
The way TIBS deploy buses is a little different from SBS Transit.
Many can observe that SBS Transit has better buses for most trunk
services and most feeder / Townlink services are single deckers
(except a few) or with older buses.
Many of you would think, why TIBS feeders or Intratown services
have all the new buses? The answer is simple. TIBS simply put buses
onto services when they feel the need is there. Just for example,
when the first Habit buses came into services, the services with
high demands or without Bendy buses got it first, then slowly to
other services with Bendy buses. Just like the case of service 811,
the 122x, 123x and 124x buses are on it because they have the need
when these new buses are put into services. The same logic applies
to service 963 when it was rebranded Trunk from Express.
There are other circumstances where TIBS put buses to beef up bus
services when the new buses are available for revenue services.
Therefore the new buses ended up on the services.
Of course, there are many more circumstances which I do not know
and some of them with same logic applied to SBS Transit, popular
services get the newer buses.