Older Mint Sets - Flat Packs

Question for all the old-timers on the board who may remember these firsthand, when the mint sent out the flatpacks, were the envelopes inside with the coins in it sealed or not?

Reason I ask is that you see people selling "Unopened Mint Set, Potential Valuable Coins" all the time. I know that is generally a rip, but....if the sets did come in sealed envelopes, is there a possibility that they really never have been opened?

I think I heard they came in the envelope, but it was not sealed. I am looking for confirmation of this. Personally, I would open each and every one I had before selling them. Doesn't make sense not to.

Thanks
Jim