I didn't really cover a couple aspects of this issue.
- I make it a point to know the expected lows as well as the record lows. Then I plan for survival with some discomfort at the record low and comfort with clothing supplementing the bag on the colder nights at the expected lows.
- I typically plan to camp where it will be slightly warmer if I expect it to be colder than I will be comfortable. That means not camping on a summit on the coldest nights. Also in the mountains cold air will pool in basins so camping a little above a lake will be warmer than at the same elevation as the lake. That is typically more likely to be an issue backpacking, but can be applicable touring.