Also keep in mind that the feathers will continue to be available during subsequent events, and subsequent quarters even, and also, at some point, I think they're supposed to be available through crowns as well, if they aren't already.

But, the berries for a specific evolution will be available only during the quarter in which they're introduced. Dawnwood berries will be available until the end of the last Q1 event, then they won't be coming back. That means that if you intend on getting all evolutions, you need to get the 4 berries for each evolution during each quarter because you won't have another chance. You can always hang onto the berries even if you don't have feathers to make the nascent yet, so I would say that you'll want to prioritize berries and then feathers as you go and NEVER NEVER NEVER buy a duplicate berry at any point. In addition, even if you did have a 2nd set of feathers in your inventory, you can't create a second nascent until after you evolve the existing one with a set of 4 berries.

These indriks are collectibles so you can't evolve more than one of each kind. That's why duplicate berries are a waste. It's the same as any other collectibles in your account. You can't have 2 bankers, or 2 vendors, you can't get more than one each of any of the costumes or pets, etc. that they make available unless they make different variations available, each as separate collectible. So unlike the feathers, a duplicate berry really is a waste.