It's a shame they don't provide a list of blocked content.
A public list of what their gateway will not retrieve for you would fuel the Streisand effect...
Most people aren't aware that there are also like 20 different valid IPFS hash formats so they have to write code to generate blocks for all those variants or it is trivially bypassed. I had to do this for my IPFS gateway at my job.
AKA multibase + multihash AKA "self-describing base encodings" + "self-describing hashes" AKA https://github.com/multiformats/multibase + https://github.com/multiformats/multihash