If I recall correctly, there's a special arrangement for the station(s) on Reunion to be included in all of the Blitzortung regions because they are so isolated.
As for the distance, I log 10,000-13,000 km strikes here at USA/NY State (station 2603) from the South Pacific (Cook Islands area) several times per month. I also log strikes every few days from northern Africa, the eastern Mediterranean, mainland Europe, south of the Amazon in South America, etc. I'm sure that it is skywave propagation, which is not the most precise signal for a ToF system like Blitzortung.
It appears that the challenge at super-long distance is in having enough other stations in your home Blitzortung region also detect the strike. Some stations are registered in multiple regions, I assume as a legacy from when the grid had much less stations. As much as I would like my station to be added to distant regions to see how it performs, I've heard that the processing power required at the Blitzortung mothership is generally not worth it to them for mostly skywave strike data hence never asking.
Remember, Blitzortung is a global science/hobby experiment, not a product that you can buy, turn on, and expect to work out of the box. If you are not prepared to spend hundreds if not thousands of hours assembling the kit, hunting down local interference, and tweaking settings, I suggest looking at one of the commercial turnkey ToF products.....