Currently Discount exists in LO Web Services as a part of Payment record. It works fine, when there is an additional gift added during the registration or when the discount doesn't cover the entire registration fee.

The problem appears when the discount is 100% (free TR registration) and there is no actual payment associated with the registration. At that point it's impossible to pull the Discount information - Payment record, including Discount, returns empty.

This is an error that should be fixed as the information retrieved through Web Services is currently incomplete and misleading.