alt Hacker NewsIndeed: that would help reconcile the presumed secrecy with the fact that, also per the article, there are upwards of 2000 of these tunnel-structures that fall into this category. All across Central Europe. Aggressor knows THAT there's likely a safe-tunnel, but doesn't know exactly WHERE the safe-tunnel is, and whether it's worth taking the time to find...
For that matter—A place to stash the kids from the census-taker and the harvest from the tax man? Tuck them away, just for that day, once every so often, and pull them out afterward?
Or knowledge privileged to some specific order, whose representatives are geographically widespread but sparse within a given community?
Tax collector avoidance is actually a pretty excellent alternative proposal. From searching, it looks like a lot of the taxes were on stuff that was difficult to hide, like farm animals owned, and houses / farmland.
However, this site [1] shows several categories for taxation that might be hidden to falsify the taxation basis. Cash, Inventories, Household Goods, Luxury Clothing. Admittedly, it seems like there would be a greater percentage of items left behind in some of these locations, since there often tend to be something. Yet, for taxation avoidance purposes, maybe they're very motivated to recollect everything that was hidden.
[1] https://ehs.org.uk/taxation-and-wealth-inequality-in-the-ger...