I have replaced the default json files under /usr/share/dump1090-fa/html/db with a set I created and in previous iterations of a v3.5 SDCard image this has worked fine for my internal network, I never tested it externally.
I had cause to re-image and having set everything back up I find I can see registrations and aircraft types only when I view my site from work (external to my home network) but not when I’m connected to the internal IP address of my RPi.
I have only port 80 open to the RPi via the router, is there anything else needed?