Incomplete charts do all sorts of strange, dangerous things. An incomplete protection chart might crush its caster, or fail to protect from anything at all. The only reason you would use an incomplete chart is if you have to, this instant, the alternative is worse than the risks.

An incomplete teleport chart risks death in at least a dozen ways. The ensnaring spells and blasts of fire from the people chasing her through the forest is certain death, or else imprisonment and torture. She touches the chart-

-She's falling, falling, flailing. Darkness all around, points of light, unflinching stars. Panic. Her protective spell is straining, she can feel it being pulled taut. It doesn't snap. Wendy spins around and around and around, not knowing how to hold herself in free fall. She loses a pencil, spinning off with a spurt of air when it reaches the edge of her little bubble. She screams. She throws up. She scrambles for her chart book, barely catching it before it spins away like the pencil, and frantically pages through until her sheaf of protection spells appears - touches one and feels the strain suddenly cut in half.  She tries to calm down. It doesn't really work - she's still spinning and covered in smelly vomit.

...She'll probably be here for a while.