Documentation is generally inadequate on your general invoice form, and your receipts as well. I always need to keep very detailed records of expenses, in order to submit for reimbursement. Invoices and receipts should always show as much information as is available, including client name, dates of service, diagnostic code, name of service provider, address, contact info, etc. Too much info is far better than not enough. A receipt should have a PAID indication near the bottom.