If a discount is not populating in the proposal there is a way to check on this
Go to settings > Pricing > Discounts
Check to see if the discount has been added to the pricing model. The "In Use By Models" Column should have a pricing model name.
If the column says "Not In Use" click Settings > Pricing > Pricing Modules
Select the pricing model you want to add the discount to, and then add the discount in the discounts box and click save.
Return to the proposal and click update pricing.