Khandro, I have never disputed the fact that Alex Salmond used the phrase, "once in a generation opportunity", in 2014. Indeed, I actually said so in my first contribution to this thread at 16.47 on Tuesday! Perhaps you overlooked it.
What I am still waiting for is you...or anyone else...to provide any shred of evidence whatsoever that the statement in any way constitutes a "promise".
Promises, in general, are preceded by the word, 'promise' or 'pledge' or ‘warrant’ or any similar word which a thesaurus might provide. No such word is present in association with the statement we are discussing here.
In any case, no party leader has a right to guarantee a future leader will feel bound to carry out his/her promises once he/she has left that position. Would you like Boris Johnson now to be compelled to carry out Theresa May’s wishes? And, if not, why should the SNP now willingly dismiss their very reason for existence…Scottish Independence…because they had one opportunity - six years ago - to put the question to the Scottish electorate?