Opinions: What is "best practice" to retrieve just the right paper when needed? See details below...

Hi there.

Let me explain. I use Papers2 to dig for new literature and manage all my pdfs with it (did so since way back with Papers1, too). I generally add a new paper when I get some journal notification email and think a given article might be usefull (not reading it right away, often too busy) or when I'm hunting down a certain topic (might read them right away, all forgotten two weeks later).

I usually come back to Papers when I'm about to write a new manuscript and I love how I can search and file all those hits from Web Of Science with Papers2. All good.
The problem is that, when writing a new manuscript [which is now and I'll try to use Citations, thrilled], I often cannot remember in which paper of my library a certain fact was stated (often a collection of 3-5 papers)... An example form my field of research: "N2O emission from soil was found to increase with temperature" (3-5 citations)... A statement like this is often not the key conclusion of the work (not in the title or abstract) as many of these kind of topics are covered in any of those publications...
For this kind of stuff it's very hard to just search the pdfs as the search terms are really generic. The keywords I have in my library are so cluttered (maybe from far-from-perfect imports or just plain bad keyword selection in the papers). So now the way I would have to deal with this is to basically cross-read every single paper which contains N2O (couple of hundred in my library) and then search for e.g. temperature which is really generic etc. ...
This is of course not pratical and I often find myself using the same "standard" references I used before (neglecting a massive amount of other possible sources) and I can easily remember.

How do YOU deal with this? Not a problem for you? Do you create keywords for each and every aspect of a paper right wenn you read the pdf (how deep do you traverse)? Right when you import it into your library? Do you use external programs like preview.app which give you a graphic indication how often a certain phrase comes up in a document and where (I mean the bars to the right when you search something there)...?

Would love to hear your opinions! Maybe it's a non-issue for you guys?

Cheers,
christian