Yes, there is a difference in the two scenarios.
Q1. I bought the house, and rented the whole house out for two years, then lived in there for six years before I sell the house.
A 1. You have to prorate the gain. 2/8 (25%) of the gain is taxable plus depreciation recapture of the depreciation taken or should have been taken ("allowed or allowable").
Q. 2. I bought the house, and rented two bedrooms out but still lived in it for two years. Then the tenants moved out, I lived in the house for six years before I sell the house.
A. 2. The entire gain is excludable because it was your residence for the entire time. You must recapture any depreciation actually claimed, but you do not need to claim recapture of "allowable" depreciation, not taken.
