^
North Carolina posted a good amount of mileage at 70 mph in the late 90s into the early 2000s. Parts of I-95, I-85, I-40, I-77, US-64 / US-264, etc.
It has been expanded to some degree since, such as the examples you listed.
US-17 near Elizabeth City was increased to 70 mph (from 65 mph) in 2007, and I believe near Windsor was opened with 70 mph in 2008. In contrast, however, near Edenton was kept at 60 mph and 55 mph over the bridge until around 2013 when both were increased all the way to 70 mph.
Newer stretches of freeway in eastern NC have opened recently with a 70 mph limit immediately, such as US-17 around Pollocksville, and NC-11 around Greenville.
Then cases such as US-17 near Maysville and NC-148 near Kinston that have been restricted to 60 mph.
There’s no consistency.