The Discounts page will display price_rule.title instead of discount_code.code
API
Effective August 07, 2017
Currently, the Discounts page in the Shopify admin displays discount codes based on the value of discount_code.code. However, as of August 7th, 2017, Shopify will display the price_rule.title value instead. Please take this change into consideration if you have an app that creates or modifies price rules.