Aircraft, air, and sound file overwrites

Greetings Friends,I've spent yet another day installing more scenery and aircraft. This has led me to a couple of questions for which I'm hoping someone out there can provide enlightenment. Question 1: Some time back, I downloaded a number of .air and aircraft.cfg files to replace the default files. When I finally began installing these files today, I noticed that in many cases I was being asked if I wanted to overwrite files that had been modified yesterday, yet I have never flown the aircraft (the Boeing 777 being one example). How could these files have been modified if I don't ever fly the plane? Do other aircraft alias to certain .air or aircraft.cfg files? The reason I ask is that before installing these files, the Dash 7 flew great. Now it has a slight, but persistent, bank to the left that requires constant correction (and it's not due to the wind). What gives? I tried reinstalling the Dash 7, but the bank persists.Question 2: It seems like every time I install a new aircraft, there is yet another FSSound.dll that comes with the installation. I'm always concerned that overwriting the old file might interfere with one of my existing planes, yet everything always seems fine when I use the newer file (although in some cases the file is actually older since I'm installing some planes that have been around for a while). As above, what gives with the FSSound.dll files? They must not all be the same, or the developers wouldn't keep packaging them with their releases, would they? Now before jumping all over me about checking the archives, I did. A search for aircraft.cfg alone bring up 40 pages worth of threads, which would take forever to sort through. So I'm appealing to some kind soul out there that wouldn't mind going over this yet again. thank you for your help.