If clauses - if + past + would have?

CONVENTIONAL GRAMMAR:

If you understood, you wouldn't say that.

If you had understood, you wouldn't have said that.

In countries where English is taught as a second language the above alone will score in the exam.

MODERN GRAMMAR offers more flexibility, like:

"If you understood, you would not have said that (or you wouldn't say that) - as the situation warrants.

I tend to support the modernists here, because while learning Grammar in Indian schools, I used to be surprised having to learn 'reported speech', like,

She said,"I will help you" She said that she would help me. But the sense is that 'She will sill help me.'

If we wrote, "She said that she will help me" teachers wouldn't get us marks.