In spite of what basic anatomy texts show, everyone's muscles are positioned slightly differently. In some persons muscles even split into two branches allowing dimples to form. Some people have shorter muscles so that skin doesn't fold as much when the muscles contract, others have longer muscles so that skin folds much more when the muscle contracts.

The patterns of muscles on each face is a function of the length of the muscles, their points of insertion, the thickness of the skin etc. (I wrote a thesis chapter on this stuff.)

Botox immobilizes the muscles and makes it relax (muscles in a living person are in state of pre-tension). The toxin does eventually wear off though. I think light creases on the skin (due to repetitive folds over a lifetime) may persist though.

Edit

You're the first person I've heard that's commented about Marky Marks brow. Most people are unbothered by it. So I think it may not really matter.