Maybe someone stole it. Maybe your mom just can't remember. Maybe some other freak thing. But it brought back something to my mind:

A zillion years ago, when I was in high school (1964? 65?) my best friend's sister got married, and the family hired me to come tidy up the house while they were at the reception.

I got a call later (don't remember if it was that evening, the next day, whenever) that they were missing an envelope with about $200 in it. That was a pile of money back in the sixties. They asked if I'd happened to see it anywhere, seeing as how I was the only one that had been in the house while they were gone and all...

I hadn't seen it, of course, and I was MORTIFIED as it dawned on me (and my parents) that they suspected me of stealing it! A couple of days later they called and said they had found the envelope amongst some mail or something, and they CERTAINLY hoped I didn't get the impression they thought for a moment that I had taken it!

Well, of course they thought that. And stranger things have happened. People steal things. It's very possible that it happened to the chain. But I still remember how that hurt. What if the money had been thrown in the trash accidentally and never found? They would probably still think I'd stolen it.