[dasil003]

IANAA, but my assumption is that that is why they update the tables every year— we always have young cohorts with incomplete data, so the best we can do is extrapolate from the past. Given a fixed cohort, over time as new tables are generated and the cohort ages, the accuracy will converge to reality. You could then look at past tables retroactively to see the error in the original extrapolations (which could be large due to black swan events).