I worked at a Kosher dairy and now work at a plant packing herbs, spices, grains, legums, pickled vegetables, sundried tomatoes and sauces (tartare, seafood and mayonnaise) that is also registered as Kosher.
At the dairy the auditor visited at least once a week and all inspections were unnanounced. Inspections were thorough. There was no formal, regular, scheduled audit. This accreditation was supplied by Adass, an organisation at a high level of being Kosher.
In my current position the audit is annual. The auditor checks the Kosher status of all of our products and ingredients. Those that are not Kosher are then excluded from our certification. This organisation lists the company's that it accredits and the products that are accredited in a booklet that is updated annually. Our new products introduced this year did not get accreditation.
I will try to answer any specific questions that you may have.
I have worked in the food industry, mainly dairy, for 16 years. I started as a Technical Officer, then became a Federal Export Inspector, then an Auditor, then Trainer and now QA Manager.