As used in these stories.
A hardened area, typically built underground, was designed to shelter people during a wartime event.
Most bomb shelters were built by governments or private businesses and designed to shelter people for a few years at most from the effects of a limited nuclear explosion; only the habitats were intended from the first as self-sustaining communities.
The consensus of experts, on the surface when it came to thinking about the effects of a nuclear war, was that most countries would be constrained over their use of atomic weapons, resulting in a limited, tactical war, one that could be described as,
"...war in which each side exercises restraint in the use of nuclear weapons, employing only a limited number of weapons on selected targets."
Larsen, Jeff A. and James M. Smith. Historical Dictionary of Arms Control and Disarmament.
(Maryland: Scarecrow Press, Inc. 2005), p. 128.
This meant that all other shelters were designed with that concept in mind, not the far worse reality in which we found ourselves. Instead, this war was brutal in its use of what seemed to be the entire stockpile of weapons all at once. It was neither strategic nor tactical.
Most bomb shelters built by governments around the world were only designed to house people for a few months. Dug into mountains, they had rooms, medical equipment and personnel and fostered the people who could go out after and organize refugees from an area that had been bombed. But, they were uncomfortable to live in, crowded and noisy, and the focus for those who survived an initial blast would be getting to and helping the survivors in the area where the bomb had hit.
Private shelters were another story, but none of them took the idea of a sustained nuclear winter into mind when designing, building or living in them. There were pricy places designed for those who could afford them, who could wait out an attack in comfort for, at the longest, five years. They epitomized the selfishness of the entitled in those waning years; most saved only a few people, the majority of the residents were older, very few were fertile which resulted in a limited gene pool with no more than a few dozen people at most in the most affordable of the shelters. The cost of most long-term shelters was out of reach for most of the population. They were not designed for long-term use, either in the number of people or in their supplies or medical facilities, which were only meant for the most benign emergencies and not the long-term care they ultimately needed.
Even within private shelters, their limited food supplies forced them up too soon. None of those shelters were genuinely self-sustaining. Instead, they relied on food that could be stored along with a small hydroponic garden to supply meager amounts of fresh food as a supplement. Others who had bought or constructed their own shelters would have come out sooner than that, no matter who they were. Be it the King of Saud or the most diligent independent person who was convinced that they could save their own family and survive, come what may to the rest of the world. Those last would have been prepared with seed and farming supplies, but it wouldn’t have mattered; the world they emerged to would have been unrecognizable, and their efforts to survive would have failed.