Not true. This is something I had researched in the early days. If you can store a crypto hash of the document on a Blockchain, you can upload said document anywhere you want for people to DL. The hashes will always match, and you can use the timestamp of the Blockchain entry as reference to veracity. This could be done via an open source project and should the maintainers fall off the map, some one can always fork.

I remember seeing this listed as something like “proof of existence”.

There’s a surprising amount of green for major cities that otherwise look like concrete jungles. There’s usually plenty of parks and kids are in general very safe. Maybe this is just my comparison from originally living in the states, but it is super safe for children and the amount of expected unsupervised travel kids do in Japan is astonishing.