I have deleted a good portion of my received PMs that are over a year old. The ones I would like to save I moved to the Archive Box. Will those messages stored in the Archives Box escape deletion or are the Elves deleting ALL messages over one year old?

It's my impression that all PM older than a year will go, so I'd save the ones that matter to you somewhere else just to be safe. The archive feature seems more like a decluttering device to save messages while not having them taking up space among your "active" ones.

Bob is correct. All messages older than a year will be deleted. If you want to save the text from any messages that are older, you're going to need to do that offline (on your home computer).