@fiddlrgrrl - I have looked at this piece and picked-out bits of it - it's not on the top of my list of things to do - but - in answer to your question - it is my understanding that the Sul D and Sul A apply only where they are shown. 

I say this - because- having listened to a number of orchestral versions, and kind-of interpreted from the score itself - the opening bars vary from almost a whisper ( ppp ) to a soft murmur ( pp )  and as the piece progresses, it becomes more and more strident / fff like  - I suspect the opening bars Sul D / A are really intended to retain that ppp / whisper-like / ethereal feel - as a lead-in to the majesty and power of what follows - just my thoughts  and I know that's not very scientific - but it's how I understand it as of now.....

Good luck with it !