If you're talking about IMAGE it was known where it was NASA just didn't know that it was still transmitting. IIRC the discoverer actually used the orbital elements to determine what satellite he was seeing. They still had an active and accurate TLE for it they'd just stopped checking because NASA thought it was dead in space after the eclipse a couple years ago failed to reset the broken power supply. [0]
"the thing about the dods tracking capabilities" is true. They know what's up there, down to lost tool bags.
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.)
My point was that the NRO had the resources to build two Hubble level telescopes that no one knew they had until they handed them over, an agency with little oversight, large amounts of cash and very few leaks.
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.
Hubble's tech isn't particularly impressive any more. NRO having 2 spare is more a sign of just how much money is sloshing around over there than anything else I think.
[0] https://skyriddles.wordpress.com/2018/01/21/nasas-long-dead-...