I've been reading through PCI compliance rules to see if it is ever PCI compliant to display the full credit card number on a webpage to a user. I've found some info about paper receipts and rules dictating which digits are visible in the card number. But there is also this blurb from the PCI Security Standards Do's and Don'ts document:
Do not store cardholder data unless there is a legitimate business need; truncate or mask cardholder data if full PAN is not needed and do not send PAN in unencrypted emails, instant messages, chats, etc..
In my scenario, I have a PCI compliant way to accept card information and a PCI compliant way to store this information (through an external site). I'm wondering if it is PCI compliant to display this information to the merchant that will be processing this card with their own payment system. They would view this information after logging into a secure site with the data being retrieved from another site through an HTTPS GET request.