You can't use the shed skin to tell how much a snake has grown. YOu'd need to weigh or measure the snake itself. If that's what you did, then I misread, sorry.
My one cornsnake rattles her tail too. She gets all full of herself. I think it's cute.
Sometimes snakes will grow slower, then suddenly take off in a growth spurt. If you can up the size of the prey that is usually preferable to increasing frequency of feedings.
The skin is sooo stretchy though, that it may be much longer or shorter once shed. I have a near 7 foot ball python shed(or did, the cat ate part of it) and I KNOW none of the ball pyhtons are that long! LOL.
Wolfy