If you are a CC Pass subscriber, you can use out-of-season Covet Collection garments on all Style Challenges, including Challenges where the season is locked.

To use your out-of-season CC garments:
Filter for Covet Collection garments on the styling screen.
Then open your filters and scroll down to the 'Season' filter (right below the 'Brand' filter).
From there, you can individually select all the seasons then tap apply!