You're right that it's a continuous thing, not just reaching a particular number. The early boomers are a big enough cohort now that them being a few years older makes a significant difference in death numbers compared to the average of last 5 years (and ABS skipped 2020 being atypical). In fact risk of death increases faster the older you get, so as the decade progresses we'll see bigger increases and exceed a trailing 5 year average by more than we do now.