Norwegian knew the APD situation when they started the routes. I'm told that they had apparently under-estimated the impact this would have ex US in particular, where they started to sell the same lead-in fares ex PVD and SWF to EDI as for DUB, ORK, SNN and BFS but of course, APD has to be deducted ex EDI. Unsurprisingly their yields are far stronger at the other airports than EDI, therefore capacity is being switched across.
They knew the score when they launched but missed a beat by recognising the impact of APD - and you can hardly blame the Scottish Government for that one.