Salv,
There is no severe/normal service intervals for GMs (or for Fords with the IOLM, for that matter). All of that is taken into account by OLM.
More severe operating conditions such as below optimum oil temperatures caused by cold weather operation, short trips, extensive idling, etc. cause the OLM to "tick" down quicker. Many posters here have commented on observing their various GM OLMs clicking down much quicker in the winter than in the summer.
That is why I always make suggestions concerning a GM OCI in context of the OLM %, as opposed to mileage, aka reducing it to 50%, and incrementally adjusting up 10% each time, for instance.
GMs OLM is a great system for the most part. I wish all vehicles had one. Then you pick the oil of your choice, within warranty parameters of course, and "dial" it in with the OLM.
Take care,
Gary