Top secret until 2073 is no less than a cover up.
One sure wonders what it is that is so embarrasing/frightening that it has to be kept hidden until there is nobody left alive that can take an interest.
Not necessarily.
In this case I don't know what has been sealed, but often a long timeframe relates to privacy laws, e.g., raw CVR recordings, health / toxicology records of the crew, etc.
From what I've seen, everything alleged to have been "covered up" (e.g., crew actions) were actually covered in detail in the official Portuguese (and English translated) accident report.