I'm just guessing here.

If you are flying a small cabin corporate, strictly domestic, Mode C, and have blocked with the FAA, nothing shows up.

If you are a large cabin corporate and bigger, fly International, have Mode S, blocked with the FAA, you will still show up because of the ADS-B feed.

Just as the airplane spotters line up and take pictures as the GV lands in the UK, there is a network of people who keep up a database of Mode S indents.

That worldwide database is used by the ASDI types.