Sure thing, CPT. I'm finally feeling less under the weather, so up for a bit more ramble.
Yes, these are rare typewriters. There's a story behind them, but I don't know it. What I do know is: that sticker is when IBM installed the typewriter on site. Yes, there was a service engagement to install and set up the typewriters, and that sticker indicates the day it was done. The green is actually a very specific shade defined in MILSPEC or something. Reason being, the primary, and almost exclusive customer, of the 50th? Is the US government.
Otherwise, it's a completely standard IBM Selectric. But the case makes it rare as hell.
As to value, I honestly have no idea. I'm not a typewriter guy, but I do keep abreast of IBM trivia and tidbits. (I have the front door assembly from an RPQ'd 7017-S7A out in my garage.)