Flat Pack US Proof Sets How To Tlel If They Are Original

Proof set envelopes were not sealed at the mint or at anytime before being shipped originally. All sealed envelopes have either sealed themselves over time from moisture in the air or by sellers trying to call them "original sealed proof sets", so there is no reason not to carefully open them.

I would open them carefully and check them out to make sure that they are the real deal.
Then put in the listing that you have opened them to check their authenticity.
I think most collectors are more concerned with getting the coins they are bidding on than a pretty envelope.
From what I can gather there are a lot of these being sold with the contents altered and resealed.
I would be a lot happier if someone checked them for me and vouched for their authenticity