Well hiding bunkers tends to be a very basic tenant of them so I assume they’d go to great lengths to conceal where exactly such bunkers are beyond being in a vague 20 mile region.

Secondly I’d assume they be might be clever enough to think to conceal the vents. To put serious resources into hiding them a distance from the actual bunker in say fake houses or office buildings that have a concealed level in the attic or basement with an intake. All kinds of ways to hide these things that would require extensive search to locate and maybe equipment.

One should assume they’d also conceal the entrance, also a common thing for anything but military bunkers. Could do that to fake buildings, a wall in a basement of a house that opens or even something more elaborate like an elevator that pops up from a concealed space in an area people wouldn’t look which you cover with a layer of dirt to hide the signs of until it’s first used (or just put it in a fake closet or bathroom in a building).

All of which is to say the wealthy have good reason to feel this wouldn’t necessarily be an issue. People assume that the rich would run into these things to hide from a successful worker’s revolution when that’s not IMO what they’re for (that’s what the bunkers tech billionaires build in New Zealand are partially for being remote, on an island run by a pliant settler-colonist state). These are for mythical things like an asteroid impact, solar flares, or more realistically instigated nuclear war that the US government informs important people to shelter from an hour ahead of time. Maybe for things like a proletariat uprising in a given region ala BLM summer type situation where people are trying to Luigi CEO’s but don’t really have the ability to completely control an area for an extended period and without a vanguard party would at any rate mostly target visible banks, homes of the rich, police stations, etc.

If they set off nuclear war (a real fear I have that they’d rather destroy most of the world rather than give up power) and nuke China and get nuked back they also won’t have to worry about that many people being around to try and kill them and those who are around will probably be so messed up with grief, pain, hunger, and other immediate needs that they won’t dedicate the resources to finding and killing people in bunkers if that information even still exists (hall of records could be destroyed entirely or at least thrown into disarray) because they’d be too busy trying to survive. At least for the tech billionaires they do tend to surmise in their planning that they/their servants/guards/remnants of the state apparatus of violence will be able to emerge eventually and re-assert order under their control of course and that’s something that obviously could go wrong for them but it would potentially buy them the ability to survive the immediate threat and even be rescued if some elements of the state still survive (as is likely in a situation where they set off nuclear war intentionally as the government has their own bunkers as well as remote military bases not worth being hit by an enemy nuke) the bourgeois state might rescue at least some of these people to manage their rebuilt society or at least that’s what they’re banking on.

Presumably a bunch of robotic turrets