add_cow_majors() for state-year obs after 2016

[rochelleterman]

Hi,

Thanks for the great package. I noticed a big when trying to apply add_cow_majors() for state-year obs after 2016. For all states 2017 and above, cowmaj is assigned 1.

create_stateyears(system = "cow", mry = TRUE, subset_years = c(1900:2019)) %>%
  add_cow_majors()

I would assume the proper behavior would be to carry over 2016 values or else assign NA to all obs > 2016.

[svmiller]

This is a good thing to note. Given the nature of the data, I don't think it's problematic. But, it's good to note and to give the user the option of honoring the temporal domain of the data.