I finally got a chance to look at all three of my snakes and I would almost have to say that this is kinda normal.
When you first posted, I knew that my first snake had something like that, but sorta different than yours. The scales on the top of his body have a line almost like a ridge running the length of them and the ones on the side have a curved almost like an indentation running along the top edge. He has a few scales in at least one patch that the whole scale is sort of indented. The ridges and curved indentations are pretty subtle and can only be seen in good light, so maybe people just have never noticed them on their snakes before.
I have 2 new snakes that I have only had for 2 weeks now and today was the first day I could take them out for further inspection. The amel, aside from numerous damaged scales that I'm presuming are war wounds from being fed live, has various lines and indentations on her scales too, more similar to what yours has, but not so regular as to run 3/4 of her length; they are more in patches here and there. The anery has markings on his scales, too, but to a lesser extent. He looks like he's going to shed soon though, so they may not be as obvious because of that.
Since all 3 of my snakes have something like this, I'd be inclined to think it's pretty normal.