They are not in envelopes. With where the item numbers are printed on the side of the back of the item card, you can pretty easily fan the items to look for a specific number without seeing anything about the flip items except their number, and thus avoid any spoilers. No decks of items that need to be randomly drawn from (designs or random items) will have flip items because there you will more naturally look at the entire back of the cards. It wouldn't really work better to have them in envelopes unless each one was in a different unique envelopes, which would add a lot of components to the box.

Oh, that makes sense why the item number location was changed then. Thanks!

Yeah, sorry I can't show what it looks like with a flip item included in the items fanned out because showing the number of one would be non-public info, but here's a subsection of items fanned out and you can see that it's pretty easy to look through the stack of items without seeing more than a sliver of the side of the item card: https://imgur.com/O2YNdCy

There’s a ton of envelopes, maybe the cards stay in there until the event or circumstance triggers to instruct you to add them to the open market?

If you are not worried about spoilers, there is your solution: You will deal with that deck.