[0] https://skyriddles.wordpress.com/2018/01/21/nasas-long-dead-...
The instances you're thinking of are either "lost" as in "presumed dead" (like IMAGE) or non-Earth orbit probes (like ISEE-3). IMAGE was never untracked, and ISEE-3 was never supposed to be tracked (but its location was still known.)
Remember when the NRO gave NASA two space telescopes no one knew they even had, bother where comparable in scope/complexity to Hubble.
The only reference I can find for this says the NRO satellites won't be launch till 2020. They're not up in orbit.
[0] https://www.space.com/16000-spy-satellites-space-telescopes-...
If they are handing over that kind of technology I wouldn’t rule out them having some amazing tracking stuff we know nothing about and won’t for a decade or two if ever.
It's just an expansion of their mandate happens all the time. Instead of creating a whole new department just to regulate launches adding it to the department that will be issuing a license anyways (anything worth putting up is going to be transmitting down so pretty much any launch will have the FCC looking at it already).
As for the rest it's really hard to do much of anything covertly in space, if it's above the size of a softball the DoD will pick it up on it's space monitoring sensors. Same thing with changing orbits unannounced they'll know within at most an orbit when the object suddenly is not where they expect it to be.
In the end the answer is could you? Yes, theoretically. But you'd have to find a launch company willing to host you and prey you have somewhere good to hide/a host strong enough to protect you because you're going to piss off every single country with a space program.