That depends on one's interpretation of a comma 😁 but I see your point.

Nevertheless, the dual carriageway is longer than 318 metres, and if *at least* the section of Fountain Hill as described in the speed limit order is considered to be the C108, then that means at least some of the dual carriageway has to be C108. So I still think it's got to be one of the two options suggested above. One is supported by [the aforementioned copyrighted source], the other is supported by the brackets on signage at the A522 roundabout.