Here's an oddity: a Sears Silvertone guitar made by Kay (usually they were made by Harmony). It originally came to my attention because it had a ply back:

It turns out to be a Kay, as evidenced by this headstock shape:

If my sources are correct, Harmony (owned by Sears since the Depression) didn't initiate its Silvertone instrument line until 1954. Silvertone was originally Sears-Roebuck's record label, and later evolved into an electronics line. In other words, this Silvertone predated the main Silvertone string instrument era altogether. 

Considering the decayed buttons and so on, I figure this beast was made after the war but before 1954. There's probably a small story here. Everyone in and around Chicago contracted with everyone else, which is how you ended up with National necks on Gibson bodies, and so on.

These are Klusons with the dreaded ICR (incipient celluloid rot).

Here's a closeup of the edge of the back. Note the three layers. The outside is some maple lookalike, probably birch or basswood. Center is probably basswood. The inside appears to be a spruce lookalike, which would enable someone to use that side as a top in a different application. 

Photos courtesy of the owner, John Yungbluth.

While we're looking at plywood. . .

Here’s a good photo of a typical 3-ply laminated top, it’s from Kenny Beard’s Selmer Saxon. Spruce on the outside, cream filling on the inside. Well, some kind of other wood. Perhaps it’s basswood, or some tropical stand-in. Usually this sandwich filling is some sort of mahogany and is thus darker than the spruce layers. This blonde wood really shows up. Some guitars, older Yamahas for example, use (or at least once used) spruce in all three layers, which makes seeing the middle layer rather tough; you really have to look closely to see the darker annular lines in the crossed-grain center layer. I think it may also account for why those old plywood Yamaha flattops tend to sound better than other laminated instruments.