On the contrary, I did answer your question. BristolCardiff and CardiffSwansea were installed on my system on April 9, 2020. SouthWales01 and SouthWales02 were installed November 27, 2020 when they came out for general purchase, automatically installed since I have the original version. As I already answered, BristolCardiff and CardiffSwansea both include licensed trains while SouthWales01 and 02 do NOT have licensed trains. That is literally the difference.
The Class 150/1 I mentioned is a separate DLC that IS for South Wales Coastal – see https://store.steampowered.com/app/448184/Train_Simulator_BR_Class_1501_DMU_AddOn/ and the scenarios designed for the original route and the link not working for that version.