Hello! We just developed an app for excluding tags from smart collections - https://apps.shopify.com/advanced-custom-collections
I think this will be relevant in solving the issue as you can create a collection that combines any smart collections while excluding any products which are tagged 'sale'. Then you can create a discount code just for this non-sale collection. Also it auto-syncs so you don't have to worry when you update or add products.
Please try it out and let us know your feedback!
Use something like smart tags to do the same thing automatically. I have set it up that as soon as its a discounted product it gets added to clearance. The smart tags auto assign 'notclearance' tag to everything that isn't in this collection automatically and a 'not on clearance' collection uses that tag to generate its products.
I have over 3500 products and it works a treat.
So, I may be missing something, but I have solved this by creating x2 tags : Discount-YES & Discount - NO
Then tag all products with one or the other
then create 2 Collections (which are hidden on site - eg. not in any navigation) called Discount Yes & Discount NO (and set auto to include by the correct tag)
Set discount codes to Applies to Collection Discount YES
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