How do you motivate designers to "flesh out" the full wardrobe/back catalogue?

If the workflow for adding new clothing sets is as slick as the frontend, I can see how it'd be easy to keep things up to date, but it's something else entirely having to go back through multiple seasons trying to remember which items composed an ensemble.

And (not knowing much about the fashion/clothing business) is it reasonably easy to swap out some items for similar looking ones if the original is not available (or too expensive), or do you face a problem where sometimes they just stop manufacturing things and there's no good substitutes?