Looking at the Star Alliance upgrade chart, 25K miles/points required to upgrade to Business from a Y or B ticket to Business, though SAS offers upgrades on the same basis on its S-tickets. Researching online, I found that S-ticket is Premium Economy (SAS Plus) but could not find other info. I was unable to book an S-ticket on flysas.com. Is this a non-discounted Premium Economy ticket? Bookable only by calling the airline or using special software? Assuming one books such a ticket, is it difficult to upgrade to Business using miles/points? (USA=Europe for example).

I have friends who flew SAS Plus LAX-ARN and were upgraded to Business at the airport, it seems Economy is often oversold, so they upgrade some of the Plus passengers to Business to make more room in the back of the plane.