Bal corrects an expression, but not every completed legal act can be undone by a correction. The text contrasts performative speech with reporting or acknowledging an obligation.
«أنت طالق واحدة، بل ثنتين»
You are divorced once—rather, twice.
«له علي ألف، بل ألفان»
I owe him a thousand—rather, two thousand.
In the historical divorce formula, the book says the already effective first utterance is not cancelled and treats the total as three. In the debt admission, the second amount corrects the first, giving a total of 2,000, not 3,000.
The difference depends on whether the first words have already produced an operative legal effect or are being corrected as a report.