Just opened the box today, and starting dusting my poor, filthy, rusty, Goodwill-shipped baby off. The serial number tells me she was made in 1916. One of the first things an initial wipe-down showed, however, was that while the red-black ribbon selector keys and shift keys are glass (with a nice little "ting" when tapped with a screwdriver), all others are a thin plastic material over a thick paper-covered cardboard, and a number are in quite bad shape--plastic broken, cardboard gouged, etc.
The machine has clearly been refurbished/overhauled at some point in its working life, possibly more than once, and the patent numbers are painted over. The plastic surfaces of the keys were also restamped/recoated at some time, as the recoating has worn off in spots.
My question: did Underwood typically manufacture a mix of glass and plastic in the same machine, such as appears here? That is, are the plastic keys as original as the glass, or are they likely to have been replaced during one of the refittings?