Actually, it was Tilly who mentioned that Federation records showed the Khi'eth was sent to investigate a 'Dilithium nursery' within the Verubin nebula. So yes, both SF and the Federation knew where the ship was. The distress call ALSO mentioned the USS Hiraga Gennai contacting the Khi'eth 6 months before the actual distress call was sent and was supposed to reach them in 2 weeks, but was presumed destroyed trying to penetrate the nebula's radiation. A SF ship find out about Khi'eth (due to being relatively nearby), but never reached the ship probably as it was destroyed by the radiation when entering the nebula. This raises a question why hadn't Starfleet in those 5 odd years before the Burn sent another ship with sufficiently strong shields/system to rescue the Khi'eth? 1 attempt and that's it? No other ship received the distress call? The Khi'eth was obviously designed with strong shields and hull due to the nature of its mission (which is why it was able to enter the nebula and survive it for such a long time), so another SF ship could have been outfitted with necessary modifications (but by the 32nd century, you'd expect ALL SF ships to be immune to such nebulae), or the USS Hiraga should have known what kind of damage the Verubin nebula could do to a ship. Anyway, I guess we could postulate the distress call which was sent after the first failed rescue didn't reach anyone as the radiation may have damaged the equipment on board to a degree that it ended up distorted as it was leaving the nebula - and it was said the distress call was distorted by magnetic interference (from what, we don't know)... and by modulating the 'music' to the lowest frequency passing through the nebula from a neutron star, the Disco crew were able to extrapolate the original signal. Well, that leaves things on USS Hiraga, which may have been in continuous contact with the Khi'eth anyway due to the nature of the ship's mission, and if they were on route, why wouldn't the Hiraga then inform SF/Federation the Khi'eth was stranded so they could be advised on what to do? And after the Hiraga was presumed destroyed, or whatnot, SF could have sent another vessel to rescue the Khi'eth.