I've gotten -3/-4 corrections while shifting on my big turbo...or over a big bump at part throttle. On my stratified tune, the knock sensors are a bit sensitive...which is a good thing. If you get a huge correcting like that, usually it is the ECU seeing two knock events in a row, so it pulls a lot of timing. No big deal unless you see that under boost in the middle of a pull. This is almost always environmental noise that trips the knock sensors.
I bet if you log whenever this happens, you'll see like 6 knock events all at once (like, one or two per cylinder)...then absolutely nothing after.
The knock you want to watch out for is getting constant corrections like that in a pull...where it starts off at zero then starts pulling timing when under boost because it keeps seeing knock events. That usually means something is wrong.
If you haven't yet, it would be a good time to swap plugs just for shits and giggles. Grab pre-gapped step-colder iridium plugs, or gap them yourself to .026". Very quick to do, just x8 of 10mm bolts, unplug the coil packs, then you need a magnetic spark plug socket and an extension. Takes 10 minutes if you are quick. Torque on the plugs is like 10 ft*lbs or something low like that. Just make them snug, not tight.
