The story asserts the landmarks changed, but can't you pick landmarks that won't change? Better yet, use GPS and grab the Lat/Long.
With geocaching, you've got something to look for. You get close-ish and then do an easter egg hunt. When it's beneath the ground, it's really hard to "look". Finding easter eggs with a shovel ain't my cup of tea.
In practice, though, I've spent a fair bit of time trying to re-occupy sites taken with handheld GPS receivers. (I'm a geologist -- it comes up a lot) 30m is a better representation of typical repeatability for a consumer-grade handheld unit or a phone.
You're often on the side of a hill, so you can't see the full constellation. If you don't have line-of-sight to more than a few satellites, you risk an inaccurate location. You're often in highly remote areas, so WAAS doesn't always help (it's based on proximity to a ground station). If you don't have WAAS, you're at the risk of atmospheric effects significantly affecting your accuracy.
There's also the user error side: You might have the handheld set to display in NAD27 one time and WGS84 another, which can easily offset the same lat/long by several hundred meters.
+/- 3m with consumer GPS is definitely possible, but that's for ideal conditions. You're rarely working with ideal conditions in the field.
Weather conditions can make a big difference. In stormy or rainy weather I was lucky if I could get +/-20m
Of course, in a SHTF scenario, GPS accuracy will start to degrade fairly rapidly as soon as the control stations are gone. So your point about not being able to return to the same spot is certainly valid.
[1] https://en.wikipedia.org/wiki/Real-time_kinematic
[2] https://learn.sparkfun.com/tutorials/what-is-gps-rtk/all
https://www.nytimes.com/2019/07/19/business/safe-deposit-box...
That doesn’t seem like much, but in a few decades your hole is going to need to be pretty big.