David Bradley as the First Doctor?

If there is officially no canon, how can those events be officially canonical?

Because they were referenced in Night of the Doctor.

But still a part of TV Series continuity.

Frobisher has to be canon because the 8th Doctor's audio companions are and as you pointed out, Frobisher featured in a Big Finish audio.

That makes a difference how? It was initially available on Iplayer as opposed to the net in general, and that's the BBC. Broadcasting is broadcasting, and you need a TV licence to legally use it

My point is there is no 'official' canon. The BBC cannot say what is and is not canon, unlike Lucasfilm can for Star Wars, so thus officially there is no canon. It's literally up to the individual's interpretation. Personally I take The Night of the Doctor references to mean Big Finish is canon with the TV series, however that's just my take. There is no official stance. 

Ah yes. I think! But why should BF be on a primacy level and the comic strips not? Even as far back as The Second/Third Doctor, there were links between strip and television - Jamie as an established companion, events occuring in the comic strip between The War Games and Spearhead from Space - don't these things elevate the comic strip to canon?

Ah, fun debate!  I'd argue no, (not that I'm arguing for a set canon anyway!) in that the comic events aren't referenced outside of themselves in "Spearhead..." or later on any broadcast episode, whereas in NOTD the BF material IS referenced.

I'm currently taking the view, which is mine alone, that TV/BF has a primacy, and everything else has latency.  This has developed due to the simple fact that we have stories officially sanctioned that star the Doctors and Companions etc.  I'm liking the Star Wars current model re pre 2014 material, where it's all there but now classed as Legends but could yet be returned to primacy if reintroduced to the main canon, like Thrawn in Star Wars Rebels.  Again, just my own take on things.

I think, on the whole, I would agree with that. It seemed to take years for BF's output to be accepted as anything other than 'fan fiction' (not that there's anything wrong with that), but now, possibly even well before The Night of the Doctor's endorsements, the company was becoming more and more 'accepted.' I think everyone has their own take on what is canon and what is not, and that's probably the easiest way of things! The mistake is when some assume that their canon is the only canon.

I feel Dalekbuster's take on it is quite selective. He rejects, for example The War Machines, because it references The Doctor as Doctor Who - and yet it is a television episode, and therefore must surely be official. But that may well be a whole different debate ...