The "CAT " chart says that in 2002 is when the C-15 "MBN" Bridge engine was built, it was still single turbo, but had smart wastegate, on engine, it had pilot injection and different camshaft, plus an expensive muffler/restrictive muffler had to be installed also, on those trucks to help with emissions.

These "bridges engines" were a temporary improvement, for emissions, until CAT could their the ACERT twin turbos, into production.( I think CAT had to pay a penalty, or use "Credits" just to sell these engines, because they didn't meet government requirements, for 2002 timeframe; because they weren't ready with those twin turbo ACERT engines, yet)