Polhemus? HAMILTON MFG. CO. Typeset desk top?

Thanks for your interest, hope you are able to help me.

What is this? How old is this? Have I hurt the value by begining to refinish it? What is it's value? It has no base/legs...what would they have looked like?

This table top sat neglected in the corner of garage I rented, I was told by the owner that his dad had made it. After many years of being curious about its strange shape and very interesting pivot out drawers. I dug it out, cleaned it, and decided to refinish it. After I got it cleaned up, I noticed the metal tag on the front...apparently this was not some random woodworking project done by a carpenter but rather what I assume is a pretty important piece of typeset history. Upon further inspection, I also discovered the numbers 27, 28, and 29 carved into the bottom middle of the black wooden squares (upper right of the desk front). The black wood is not actually painted black but rather soaked in years of black ink. I can vaguely see the number 3 on one of the vertical sides of the squares, I can only imagine that there are more markings, but seeing as they are carved into the wood, they have become illegible from the layers of ink caked into them.
I have been attempting to find more information about this tabletop, but have not succeeded. I would like to continue on with staining and polyurethaning it, but don't want to do more harm to the value of the desk top since i now know it's not just some random piece of wood. I fear the sanding that i did to get it cleaned up has already lessened the value.
...that is if this piece is in fact as special as I think that it might be.

Please help me to understand exactly what kind of treasure I have unearthed. The closest thing I have found are the polhemus cabinet tops, but the are not quite it. Especially when it comes to those fantastic pivot out drawers.
Thank you for any help you can provide!!!!