Whilst I can tell the difference between regular and diet from a can, I really struggle with telling them apart in the 'fountain style' cokes in restaurants and pubs; they all taste pretty similar to me. I'm sure it has happened to me and I've just wondered 'what caused that spike?' and whacked in a bit more of the old jungle juice to cater. It is a bit of a bummer.
For this reason, if I do order these in pubs and restaurants I always test regularly as I realise that (with the best will in the world) mistakes will happen. The bar sorting out the drinks might be doing 200 cokes an hour and the chances of it being staffed by someone that
(a) realises the potential problem (even if you explain it to the waitress) and
(b) cares
is pretty slim.
Beer or (if on the wagon) mineral water is a much safer bet if I don't have a sniffer dog with me

Were I T2 and unable to get the mistake sorted with insulin, I think I'd avoid it altogether unless I actually saw the bottle / can.
Gary