I'd be tempted by a re-prompt, personally. I too am subscribed to notifications on the older posts, but not everyone is. Casual browsers will generally just check the latest post for new stuff.

Re-prompts are generally allowed once per post. So as long as it's not been already reprompted in the current prompt-post, then it's fine.

So, yeah. I'd re-prompt and fill on the current one, and link the fill on the original prompt as well.