It counted in 1976 because there was no rule about who would be eligible for nomination.
Rule 27 specifies the order in which rules are to be presented and acted upon. But those rules cannot change the already agreed upon rules during the current convention.
Rule 30 specifies that the rules of order that govern the House of Representatives will be used by the convention to conduct business.
Rule 32 specifies that those rules (i.e. The Rules of Order in reference to Rule 30) can be suspended by motion.
I am a Cruz supporter. I will vote for Cruz in my primary. I am not a fan of Trump running around saying he will sue anyone. But I would 100% support a law suit by Trump to prevent any breach of contract in regards to the convention.
But the rules established by the Republican Party for their convention is a binding legal contract and they cannot just changed the rules at a whim. They must follow the agreed upon procedure for doing so. If they attempt to break the contract, they will be forced to comply by the courts. Count on it.
Note this line in 40(b):
Notwithstanding any other provisions of these rules or any rule of the House of Representatives...
See that? That means that 40(b) is not debatable. What follows that phrase is set in stone.
It appears to me that Rule 40 is the same as it was in 2012, except that it was raised from 5 to 8 (I could not find 1976 Rules but I know the 5 state rule was in effect then).
The goal of raising the bar to 8 states was to deny Ron Paul a nominating and seconding speech in 2012. The votes for him counted.