Every year in the recent past we’ve had Spinebills spending winter around our home (likely enjoying of the native plantings we’ve had from Frances). First it was just one bird, but last year we had quite a few, there were at least four here for a while.
After being absent over summer, the first individual turned up yesterday, and it was… a juvenile.
Hope this observation contributes evidence to your theory, Geoff. And apologies for the poor photo, it was taken in low light through the front window!