One aspect of the Scandinavian charters was that, long before any EU operator could fly anywhere, the Scandinavian companies could fly from any of the countries, other than their home one. You can see this in some of the flights listed above, with Braathens of Norway operating from Stockholm or Sterling who operated from all of them. They would have a couple of aircraft based at each main city, and run them at an intensity similar to UK IT operators, down to various Mediterranean points all week. The Sunday London flights were a bit of a fill-in between these operations. It is also a Scandinavian feature, like Canada, that sun holidays have long been popular in winter as well as summer.
Sterlings Caravelles were notable for some astoundingly long-haul holiday flights they did with them in the 1970s, to Thailand (long a popular place for Scandinavia, or to San Francisco in California - the latter a bit unbelievable were it not for several photos on the web and a couple of accounts of the flights. They typically routed Copenhagen-Keflavik-Bangor-Omaha-San Francisco. They went through Bangor to and from the Dominican Republic as well - then next day the short hop to Stansted.