I don't know the exact number, but I am at 6 full binders and counting. Each sleeve has two playbills in them back to back. I can say that I do have some valuable ones though that will NEVER part ways with me.
The idea is to work and to experiment. Some things will be creatively successful, some things will succeed at the box office, and some things will only - which is the biggest only - teach you things that see the future. And they're probably as valuable as any of your successes. -Harold Prince