I can get quite an accurate measure of the "stalls available limit" from my end of the country - I just had a look and can see the status of Grantham at 298.7 miles but not Keele at 311.4. So I'd bet on it being 300 miles as the crow flies and as I have a MS 70 it's probably just a notional 300 mile limit for all cars. Now I'm tempted to use upcoming Scottish lockdown-easing freedoms to drive to Peterhead this weekend to see if I can view the live status of Vikeså (Norway): frustratingly it's just out of range at 315 mi from where I am now.
I can see the Norwegian chargers, but only see the stall info when I click on the charger. Otherwise it just shows the lightning bolt.