Mail Mystery

As a Disney D23 member, I receive a magazine four times a year. The most recent issue arrived, and it comes in a mailing box that you have to pull a tab to get at the magazine. As I'm opening the box, a surprise falls out:

I took a closer look at the letter, and it was mailed from L. Herman, in Montreal Canada, to Alan Harold Friedman in Flint, Michigan.  IN 1974.  It even has an eight-cent Canadian stamp.

The letter had been opened, and inside we find:

It's the kind of card that is shaped like a wallet to hold money.  So in 1974, Alan Friedman was celebrating his Bar Mitzvah, and Mamie and Len Herman wanted to send the kid some cash.  How nice.  But there's nothing in the envelope today.

How can this be explained?  Why would an opened letter from 1974 show up in a box that contains a magazine from Disney?  I guess we could assume that it has been sitting around some post office (it appears to have been stepped on), opened at some time and the money removed.  But then...what?  Some veteran post office employee suddenly feels guilty, and hopes that a Disney fan will make sure Alan gets his long-overdue congratulations from Mamie and Len?  Should I include a few bucks?  Should I allow for inflation?  Did Alan ever wonder why the Herman's stiffed him when he was thirteen?

Present day Google Street view of the Herman's address:

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 Unfortunately, Google Street view doesn't make it to Alan's street:

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My only solution is to notify Michael Moore.  He'll know what to do.