The ship date on your order is used for excise tax and shipper reports, whereas payment date is used for sales tax reports. First, check your order status and relevant dates to verify that they match the dates the report is pulling.

In your Report Settings, the default is to include orders with a status of Sent to Fulfillment on reports that are based on ship date. You can decide whether to keep this status on; if it's off, it could affect what orders are being included on your reports.

If your order has been completed, but hasn't sent to fulfillment, go to Orders > Adv. Search, and filter by order status. You can manually change order status from here, if necessary. The combined options (All unshipped, In process and payment accepted) can be helpful here if you're checking on multiple orders.

You can also search by invoice number in the keyword field. This can help you find a specific orders' status, and check its tracking number if it has already shipped.