It was 7 February, and SBS was showing "no signal". I then remembered that somewhere I had read that further changes of the some of the TV channel frequencies was occurring. In fact, it was an advertisement in the local paper that I had read. If it had been mentioned on SBS - the channel that, at least so far as we were concerned, was affected - then we'd missed it. [Edit - seems that this is in fact what had occurred, or perhaps we watch at the wrong times.]
The challenge then was to do the retuning. I scrolled through the menu, and tried "update". After this had finished, still no SBS (even though I got a report that 7 channels had been found - must see if we really do have anything new). Only when I set it to "install" was SBS again available.