As someone with a causal passing interest in the cold war and nuclear weapons, yes this is public knowledge. How to build a blast shelter or fallout shelter was widely disseminated in the cold war for citizens to build their own. Overpressure protection and NBC air filtration is just part of building a good shelter. The filtration systems are not some exotic radiation neutralizing material, they are just filters to catch irradiated particles and keep them from entering the shelter and being breathed in. If anything, the pictures of the bunkers showing their camouflage design and locations would be the biggest disclosure, but even that is obviously not an issue at this point.