Well, if our dear Jane mentioned it Northanger Abbey (published before the first game in America) - that settles it! :D
And Philly, I did debate the spelling of Treets with the missus - she insisted it was Treats :lol:
I've never had M&Ms, but my recollection of Treets is exactly as yours and 38th. And yes, they did melt in your mouth but not in your hand as long as you didn't push them too far - I can remember when they came out and me and my gran performed rigorous testing on this marketing claim!!