Flashman….your rule is good, you are just being too strict.
Consider this.
If Japan or Russia declares war on the other, the declaring power then may not declare war on any other power untill its 6th turn.
The doubble blind holds. Because to break the pact would mean Germany need not fear Russian intervention untill turn 6 instead of the normal turn 4. Likewise if Japan declares war on Russia, the US/UK need not fear Japanese attacks untill the 6th turn.
However flashman…these issues are merely temporal, and not strategic (though i I know strategy is an abstraction in a game of A&A’s scale)
The carrot and stick approach that NOs have put into the game realy incentivizes players…it could be used to deincentivize braking the pact.
Either
a) while you are breaking the pact you collect no NO bonuses (Because breaking the pact went against the realistic National Objectives of both Japan and the USSR, no bonus production would accumulate because of both the contradiction in policy, and the extra funding required to fight a war that was avoided by both powers)
b) a -5 NO if a power breaks the terms of the Non-Agression Pact, which are as follows
Japan agrees to not attack or occupy original Soviet Territory
The USSR agrees to not attack or occupy original Japanese Territory, or occupy Chinese Territory
The -5 NO is enforced untill the terms of the pact are restored.