Damn those rules are complicated!
Are you saying that Britain and France have to start a war with Germany if they invade Poland? Even if they feel they are not ready they must declare war?Britain and France must go to war with Germany if it attacks Poland. Any other country that subsequently attacks Poland can do so without
providing a Casus Belli (IE The USSR or the Dictatorships).
The two examples you gave (the USSR and the Dictatorships) do not need a Cassus Belli to attack any nation right? So why did you use them as an example for Poland, surely they can invade Poland whenever they want??
Its just confusing.....