I believe the gradebook is adjusting because there are some items that have not been attempted yet that have a weight to them. So for the purpose of the grade right now, the gradebook is showing how much weight that category carried towards the grade at hand. Because Final Group projects are excluded, it would make sense that their weights were excluded to. Otherwise, students could never receive over 85% until the final project was completed.
As to comparing with their excel sheet, without knowing how they calculated that, it is hard to tell. The gradebook will divide total points possible by total points attained to reach the percentage (then multiplied by weight if weighted). I have had teachers report that before and have always been able to get the gradebook within a percent of their calculations (sometimes rounding up skews off just a hair) - normally, it is a mistake in the gradebook setup.