Not exactly the route you will fly, but I've flown CDG to OSL and CPH on SK and credited to A3. In each case the mileage credited was just a few miles shy of those given by gcmap.com For CDG-OSL I got 842 vs 845 indicated by gcmap. For CDG-CPH it was 621 vs 625. I guess this doesn't really prove what you'll get but it gives a good idea. Since gcmap shows CDG-ARN as 959, I'd bet you will get about 3 x 954 = 2862 which should be OK.

Are you aware of the "optiontown" upgrades on SAS? You can usually upgrade SasGo fares to SASPlus on a "request" basis for around 40 to 80 Euro depending on how long/busy the route is. This could be quite a cheap way to ensure you get enough miles. More info here: https://www.flysas.com/en/es/travel-...chase-upgrade/

For info, I regularly credit SK miles to A3, both in O and A class and they usually post promptly (3 to 4 days). I just had one problem flight that took me nearly three months to sort out. It was one of a 5-leg itinerary - four of them posted right away but one wouldn't. I haven't tried to credit on Optiontown upgraded flight yet.

Hope that's useful.

EDIT: Since your outward fare is flexible and can be chaged for free, why don't you see if you can rebook it as two legs, via CPH or OSL to get at an extra 300 or so miles? You could probably do that for less than 50 Euro.