Our team is looking to implement new metrics and I'm a fan of capturing DRE; however, I'm curious how others are calculating DRE within their organizations? Specifically, when implementing this metric for an existing project that has already had numerous releases and has a number of existing defects in backlog, some of which will end up pushed to future releases and then probably pushed again.
Expanding on what Matt has already said. A lot depends on what the purpose of this metric might be. Without knowing that, I can't begin to even suggest how you'd track it. DRE is a known bad metric, and I've only found once context where it provides any useful information, and even then, it only showed that dev teams were focused on new features not technical debt or bug fixing.