Well there a couple things you can do - firstly, yes, you can change that - if you 'q stat' you will see Actlog Retention - that will tell you how far back it goes. I just checked one of my servers and its set to 30D also - Ideally you want to be able to go back a bit further, maybe 60D. Use 'SET ACTLOGRETENTION' ('help SETACTLOGRETENTION' will explain it better than I would)
For your volume issue - Not sure how you will get a date now... What I do to keep track of scratches is that I have a dummy tapepool that I define all my scratch vols to. When I add scratches, I delete them from the dummy tapepool (you have to delete from the dummy pool to check them in as scratch or you'll get an error). This logs a STGDELETE entry in the volhistory table in case I need to know when I added it to the library.
Again, not sure how you'll get the info now - but this may help you going forward.