I'll answer this because I started this thread. Not TMM217's fault.

CMP Retard (Offset) is a measure of the relationship of the camshaft to the crankshaft. Since the cam sensor is mounted in the distributor, it also takes into account any wear in the distributor gear. The camshaft sensor signal tells the PCM which cylinder is firing at the moment, and this in turn is used during misfire detection and also is used to time sequential fuel injector pulses. Indeed if you disconnect the cam sensor, the engine will still run quite well but misfire detection will be disabled, the SES light will be illuminated, and fuel injectors will be pulsed in two banks of injectors instead of sequentially.

Because timing is controlled by the PCM (exclusively based on the crankshaft sensor), it is possible for the timing of the spark to be correct - yet the distributor will not pass the spark to the spark plug because the rotor is not pointing to, or not pointing near enough to the correct terminal inside the cap. Fortunately, because the cam sensor is actually mounted inside the distributor, setting cam sensor retard (offset) accurately aligns the distributor so the rotor points in the optimal direction and the spark can jump from the rotor to the proper cap terminal as engineered.

Unfortunately factory Second Gen distributors have hold down brackets that are non-adjustable. With the engine on TDC#1 the distributor is dropped in with the rotor pointing to the #6 cast into the top surface of the distributor (or as near to the #6 as possible). If you get the distributor in a tooth off, you will set a P1345 code. If you are outside the cam retard spec, but on the right tooth you can experience intermittent misfires with no codes because the spark is jumping where it should not go.

If you can't check cam retard (offset) then you simply hope and pray that the cam retard (offset) is 0° ± 2°. If you have the ability to check cam retard (offset) and it is outside the spec, then the mounting hole in the distributor hold down bracket can be elongated in order to give a little distributor rotation to adjust it. Another method is to replace the hold down clamp with an old-style small block Chevy part that is not locked in place.

Worn timing gears/chain and worn distributor gear are the only reasons for the Cam Retard (offset) to change during the lifetime of your vehicle. So if it is very far off, you should probably check the distributor gear for wear. It is a common problem on the Blazers.