The site inst going to be correct for intermediate points as it's hard enough just getting the base data! The 128 is correct. I suspect the first mention of the 121 in a timetable didn't mention that it went via Lulsgate and the list of via points has copied from that afterwards.I don't think that list is quite correct and is lists Bristol Airport to Weston via Hutton as the 128, this was the 122/822. It also fails to mention the 120 which went via Shipham, the 121 and the 821.
120/121/122 family of routes here:
http://bristol-re.co.uk/bvbg/routes.asp?opt=S&IL1=3517