I have the startled pumpkin needed to complete my collection and earn the acheivement and title, yet there is no option to add it to my collection. Am I screwed because the item is retired?

if there are any new pumpkins on this Morostide, you'll be able to add them, since the pumpkin collection is for Morostide, along with any new ones, if any.

I already completed my pumpkin collection, and it seems I don't have that pumpkin. That means it doesn't go in the collection, that's why you don't have the option and maybe you're missing another pumpkin. You could create an account on Subetalodge so you can use the lists feature and see the one you're missing :)

I'm pretty sure that one isn't part of the collection.

The one you're missing is

Oh, Thank you so much all of you! I thought it was the startled pumpkin that I needed. So helpful, thanks again!