It looks like your buttons A2 and B2 copy exactly the code you used to create a1 and b1. Use an iteration to change id and names of the dynamically added buttons, so that your b button become b2, not b1.

it should look something like this
var iteration = lastButtonNameNumber + 1;
var new_a_ButtonName = 'a' + iteration;
var new_b_ButtonName = 'b' + iteration;

And then access the new b-button value using something like
document.form.new_b_ButtonName.value = ....

Hope you can figure it out by yourself.

Good luck.