Preliminary context: How is the «Payment Information» block rendered on a backend order’s page?
See also:
\Magento\Sales\Model\Order\Payment
setCcLast4()
getCcLast4()
getInfoBlockType()
The behaviour has been changed in https://github.com/magento/magento2/commit/8b06b248d313dfdb85de43c23b754d87fc1b58a0
https://github.com/magento/magento2/blob/135f967/app/code/Magento/Braintree/Block/Info.php#L14-L14
https://github.com/magento/magento2/blob/135f967/app/code/Magento/Payment/Block/ConfigurableInfo.php#L51-L71
https://github.com/magento/magento2/blob/135f967/app/code/Magento/Braintree/etc/config.xml#L38-L39
https://github.com/magento/magento2/blob/135f967/app/code/Magento/Payment/Block/ConfigurableInfo.php#L77-L97
https://github.com/magento/magento2/blob/135f967/app/code/Magento/Braintree/Block/Info.php#L16-L25
https://github.com/magento/magento2/blob/135f967/app/code/Magento/Braintree/i18n/en_US.csv#L131-L145