Missing months for select states

I downloaded all of the monthly data for 1990 and 1991 for all states to calculate state-year unemployment rates. However, when I collapse my dataset, I notice that not all states have data for all months. For example, my extract has no Alabama data for February 1977. Does anyone know what I’m doing wrong?

In some months before 1978, not all states were identifiable. The ability to identify records within states or not is largely influenced by the sample sizes (which were relatively small in 1976 and 1977) due to confidentiality restrictions on public use data. You can see which states are identified by month in the codes tab for STATEFIP (make sure to have selected the samples you are interested in first). For more discussion on this, see the comparability tab for STATEFIP.