1. The material (HOT SL Synthetic Insulation) is hollow core TNF insulation, and all their bags test well so I would assume the 20º temperature rating is accurate. in 30-40º weather, this bag would keep you warm because there's another person in it with you.
2. The bag will have lost no warmth unless it was heavily compressed in storage. Even then, probably not much- send it through the dryer on no heat with tennis balls for a few hours to restore it.
3. If you're car camping, you can always bring a few blankets to use on top of the sleeping bag!