I met this phrase:
"Il ne tint pas à lui que nous n'ayons en France, dès 1908, les fameuses démonstrations de W. W. et que le prodigieux mouvement actuel n'ait commencé deux ans plus tôt".
Source: L'Aerophile about Arnold Fordyce
Using historical facts (without apriori knowledge I would not have understood anything) I extracted a meaning from the above phrase as follows:
"It was something independent of him (it was not his fault) that we had (or witnessed) in France only (late) in 1908 the famous demonstrations of W.W. and (also) that the prodigios present movement has not started (or did not start) two years earlier (in 1906)." (This is my own interpretation, it can be wrong.)
However, I do not know why the present of subjonctive negated but without pas has the meaning of a positive and the past form of the same subjonctive also negated and without pas should be considered a negative.