So a long time ago, I was searching the internet and discovered a painting by Brian Kotzky called "Hardy Boys Avalanche". I actually posted it to HDA, I believe. It showed Frank and Joe on a cliff's edge with an avalanche coming towards them. I tried as hard as I could, but I couldn't find any Hardy Boys book with that cover, not even an international one. However, Clif-Hanger has an avalanche in it. My suspicion is that Brian Kotzky did covers for 105-112, but they never got used in favour of the TV premotion covers.
And there's some other evidence for that, I ran into an auction site that had some unused Nancy Drew Files covers from the TV covers era as well, and I believe that I posted them around the time that I was doing the Files cover poll. (Still looking around for that, will post an update if I find it).
I had saved "Hardy Boys Avalanche" to a computer that ended up with a corrupt hard disk, and it has apparently disappeared from the internet.
Edit:
http://www.synsinepress.com/art.html
unused cover art for Nancy Drew Files # 112, 113, 115
Wow! Interesting. :) 8)