There are some known issues which aren't fixable

Project Cars doesn't send opponent laptime data, so Crew Chief has to time their laps. In practice and qual sessions this is fairly reliable (because Crew Chief can use the time remaining in the session, sent by the game, for its 'clock' when timing). In race sessions with a fixed number of laps Crew Chief has nothing it can use as a clock to time the laps, so times them itself. This can lead to opponent lap / sector time inaccuracies if the player pauses the game (Crew Chief's clock is still running).
Joining a session part way through (practice or qualify session online) will result in Crew Chief having an incomplete set of data for opponent lap and sector times. In such cases the best opponent lap and sector data is inaccurate. For Project Cars, there's nothing I can do about this. The opponent lap and sector times aren't in the shared memory (Crew Chief has to time their laps), so the pace and sector delta reports may be inaccurate (they use the fastest lap completed while Crew Chief is running). For Raceroom we can get the fastest opponent lap time, but if this lap was completed before Crew Chief was running, the sectors within that lap aren't accessible. In this case the pace report will include the lap time delta, but there'll be no sector delta reports.

In both cases as soon as an opponent sets a faster lap, Crew Chief will have up to date best lap data so the pace and sector reports will be accurate and complete.

Project Cars doesn't send opponent car class data, so Crew Chief has to assume that all drivers in the race are in the same car class. For multiclass races, all pace and other reports will be relative to the overall leader / fastest car.

Project Cars doesn't have a distinct pre-start procedure phase. I've added some more messages before the 'get ready' but there's a risk here that they might delay the 'get ready' message.

RaceRoom uses a 'slot_id' field to uniquely identify drivers in a race. However, this field doesn't really work properly (there are lots of issues with it), so Crew Chief has to use the driver's names. Driver names for AI driver are not unique. All the lap time and other data held for each driver is indexed by driver name so if a race has 2 or more drivers with the same name, Crew Chief will get things like lap and sector times wrong. This is only a problem racing the AI - be aware that if you have a car class with a limited number of unique AI drivers (Daytona Prototypes / German Nationals / Americal Nationals / Hill Climb Legends / etc), but select a field size greater than this, Crew Chief will do weird things.

RaceRoom doesn't have a pre-start procedure phase for offline races, and in the pre-start phase online ("Gridwalk") very little valid and accurate data is available.

Detecting 'good' passes isn't really feasible. I've tried to limit the 'good pass' messages to overtakes that are reasonably 'secure', don't result in the other car slowing excessively, and don't involve the player going off-track. I can't, for example, tell the difference between a clean pass and a bump-and-run punt, so you might get congratulated for driving like a berk.