[altacc]

Over 60 years you would have to account for the many other factors that also affected mortality, for example better healthcare. That would increase the statistical error and reduce the validity of the results. And it isn't really necessary as long as your baseline contains enough data to be able to prove statistically differences from your comparison groups. Generations are taken into account by splitting the results by age and not looking back too many years, as even with flu, cold winters, etc... life expectancy still changes slowly.