Trying to answer my own question:
The data is not exactly the same. The number of stations returned is different.
I have 24 zones.
‘/jn sn’ returns 24 zones worth of data (zone 11 active as expected)
‘/jc sbits’ returns 32 zones worth of data (zone 11 active as expected)
Why? Is it a bug?
OK, so I can figure out how many zones I really have and ignore any extra zones that ‘sbits’ returns to work around this.
When I get more time, I’ll try hunting the OS code to see if I can find out why.