One interesting snippet is that not all companies sponsored the event in all markets. The core companies logos were shown in all of them (such as Castrol, Goodyear etc.) but some logos didn't appear on the vehicles in certain stages - this is why on the 2003 challenge the Warn stickers are on some vehicles but not on others.
I believe Snap-On is another example -although their tools were used everywhere and the logo was on the workshop vehicles, it was visible on other event vehicles in certain markets.
Being fair though that could all be rubbish, and the stickers either didin't get stuck on or fell off :D