Help with filling data in previous years and months

tidyverse
2

Well it's not elegant and not automated, but at least for your particular example you could always "manually" duplicate 2018 only changing the year:

template <- vol |>
  filter(year(Date) == 2018)

bind_rows(template |>
            mutate(Date = Date - dyears(2)),
          template |>
            mutate(Date = Date - dyears(1)),
          vol)