I think there are multiple "correct" answers here, it kind of depends on what you want to track. In the past, I have considered a click on one or more of the CTAs in the email to be a Success in the email program, and created separate content programs for each asset that requires a form completion, with success in that program for the form completion. That was revenue attribution is split between each of the components that "influenced" the person - the email, and each asset they downloaded.
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