Small projects will have small misc. This has to be based on existing activities of the project in question. It's difficult to keep track of all the uses a corpus fund will be put to, so we have to assume that the money will be put to good use. Of course, this assumption will be based on existing project activities, reputation of the organization etc. In addition, regular reports of the organization's activities will be required.
All organizations have to go through an audit.
The corpus fund is tracked during audit. Deductions from the fund and additions to the fund are kept note of. The financial records of the organization will show us if the corpus fund remains just that. This depends on the organization in question, what kind of emergencies it forsees etc. The size of the fund should be reasonable, it can't be larger than the annual budget for example.