I've got a mail from PSL today with the following explanation:
Go Show rule applies to single flights only. It is not applied to the bookings where there are connecting flights.
In case a passenger has a connection, it is not possible to benefit from Go Show. The change for connection flights is then counted as a regular date/flight change and customer would need to pay any fare difference.
But this confirms there is such thing of Go Show, at least with single, direct flights.
I'll see what happens with the app, though.