The use of type 2 conditionals for past inreal situations

A. Davtyan writes in his book, The Use of Subjunctive Mood in English

"The past forms of Subjunctive II [had done] in complex sentences are used to express prior unreal actions, whereas the present forms [did] - simultaneous with the action of the predicate verb in the principal clause i. e. they express the time of the action relatively, not absolutely."

And although this formula seems to work in the following examples

1- she thought she could die if she stayed there a moment longer

2- it was widely believed in theology that if people had wings, they would resemble angels

And so on, it yet doesn't work when one says

3- I was so angry that I could kill her (if I had a gun but I didn't)

4- there was so little food that everyone would die (if there broke out a riot but it didn't happen)

Why doesn't the above formula work in 3 and 4 but it does in 1 and 2? All of their predicate verbs of the principal clauses are in the past, yet 3 and 4 should be changed to "that he could have killed her" and "everyone would have died".

Thanks