What the article and the graphics seem to suggest is that the missing data was removed during transcription to microfilm.
...the missing data was removed during transcription to microfilm.
Once again there must be records of some kind as to when the microfilm was made and who made it.
This is the government...everything that is done is documented...even if it's hidden from the public for a time.
Government workers are good little drones and don't do anything unless they're told to.