I'll offer up a third option, which is that the envelope may have simply come unstuck in transit and deposited its contents throughout some musty distribution center, after which some "helpful" postal worker noticed it and taped it up. My wife hates the taste of envelope glue, so she licks them only lightly, resulting in them often coming unsealed again before they even leave the house, so she always tapes as well. Perhaps your sender has a similar distaste for glue.
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