Over time the cuts and holes that make up the image of a stencil will begin to fill and clog with paint. This signifies the death of the stencil.
Teacher's 'Peace Through Paint' stencil has had a long productive life with over 40 sprays being utilized before it started clogging. Here is the last street stencil of Teach's 'Peace Through Paint' stencil, with close up pics of how the paint is starting to fill in the screen.
Rest In Peace (and Paint!)~