Proof and Mint Sets Not sealed by the Mint

Were the SMS sets ever sealed? The ones I've bought off eBay are just acrylic cases with a blue insert. Is this how they came from the Mint?

 

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The '65 SMS came in an envelope (unsealed) packaged in pliofilm. The '66 and '67 came in a hard plastic holder packaged in a box.

 

The coin shows on TV sometimes sell those sealed sets at a premium. Imagine that...

 

Reviving an old thread with some questions.
Many of the mint and proof set envelopes have the flap sealed down and were cut open across the top. Why were these cut open if not sealed? Sealed at the mint, sealed by nature, or sealed by seller? Who knows? Who cares?
Buying site unseen coins has always seemed stupid to me, but gullibility has never been in short supply.

 

Because once they got exposed to some humidity and self sealed it was an neater and easy way to open them.