We take purchase history into account when choosing your next pair so the only time you could ever receive a duplicate is if we’re sold out of other options. Check this link to learn more about how our algorithm works: How do you pick what you send to me?
On the Bold and Adventurous plans, duplicates are pretty unlikely since new colors and prints are released frequently. On the Classic plan, however, our toned down and neutral colors rarely change so the chances of a duplicate are more likely. Keep in mind a duplicate will only happen if you've previously received every classic color we offer.
Additionally, if nothing is available, your Membership will be auto-skipped.