The buses were previously NAC SBST Mercedes O405 (i think their
regos were in the early 37xx range, about 20-30 of them, since
their front wheel validator area is "square-ish" and u can sit on
it, n the bodies of the early NAC O405's were made like tis until
SBST made Duple Metsec change it to curved to make it more
spacious) buses that were converted to air-con and made to serve on
Jurong Island Services (JIS). why they re-registered as PA i dun
understand.. probably not giving workers the idea that Singapore is
SBST-dominated or JIS is its own division.
When SBST withdrawn the JIS services, most of the buses were
rested, with some running on SBST 284, probalby cos it's not so
prominent, pending LTA's permission to put them back on public
scheduled services or it will be a waste of resources. and so it is
now back, also on SBST Express 502 and 518.
Regarding the re-registering of regos as SBS regos, i dun think it
does matter to SBST anymore that they can use these O405 buses
now.. probably few commuters like us will actually notice
regos!