also where can i find out more about which flight number matchers which airline, please?

The explanation to your first part has already been covered (i.e. they are all airlines selling code-shared seats on a single flight belonging to one of those airlines). On the second part, google is a wonderful monster…got to google and type in something like “SN Flight Code” or “BD Flight code” and you should very quickly find out who these ailrines are (in these cases, Brussels Airlines and bmi British Midland).