I have (3) specific coupons running (eg. A, B, C) with "Stop Further Rules Processing" set to "Yes" for all of them but if you first enter the coupon code for A and then B Magento removes A and processes B? Isn't "Stop Further Rules Processing" suppose to prevent this behavior? Also, is it not possible to prioritize coupons in the absence of "Stop Further Rules Processing" ? For example, if coupon B is entered and then coupon A is entered setting coupon A to always replace B but never B to replace A? etc.
I think you misunderstood what "Stop Further Rules Processing" means.
It means that if there are multiple discount rules valid for one cart and your rule with "Stop further rules processing" is encountered, all the other rules that should come after that are ignored.
When you apply coupon A you get 1 ore more valid rules for the current cart.
But this does not prevent the user from adding an other coupon.
If the user adds a new coupon code (B), the first one (A) is deleted and you get a new set of possible rules that apply to the cart.
Magento does not support out of the box 2 or more coupons on the same cart.
So you will never have coupon A and coupon B applied at the same time, but you can have multiple rules applied at the same time if at least n-1 rules out of n don't have coupon codes.
You can priorities the rules by entering a sort order. The smaller the sort order the higher the order priority.