For 1970, there is no data for seven states: S Dakota, N Dakota, Montana, Ohio, Vermont, Wyoming, Idaho, Delaware.
The question is why and whether there is a place to find this missing data?
There are multiple 1970 and 1980 samples, with both years having separate State and Metro samples. The difference between these samples is briefly address in on the Sample Description page. As is mentioned in their sample descriptions the Metro samples give preference to the identification of metropolitan areas (which can cross state boundaries). In these cases it is not possible to tell which state a person is in and so the state information is suppressed. This is why it seems that there is no data for some states in these samples. The State samples give preference to identifying states, so if you would like to be able to identify each state in 1970 you can select the State samples.
I hope this helps.