We're trying to create a smart list saying Email was Delivered - Email B, which was part of the A/B test (Email Program). However, the pick-list won't show Email B
Is this because the test/winner was sent to a sample randomly (based on % defined) and Marketo won't allow to see who received the Emails?
If the A/B test was for any A/B testing option except "Whole Emails", then you would only select one one email with the filter. If you tested "Whole Emails" then you can select just those that were delivered that specific email asset. If not "Whole Emails", then you can use "Delivered Email" with the constraint of "Test Variant".