Honestly I have have a hard time believing the central government knows nothing of the Terrans the more I think about it.
It takes approximately
two years by the fastest possible courier route, using max jump all the way and handing messages off to a new courier at every relay instead of waiting for a courier ship to refuel and refit, to get a message from Shalgiasu to the Imperial capital at Vland. It would take approximately
five years for a single ship to follow the same route, allowing for reasonable shore leave, resupply, and refit en route.
When Sharik Yangila mused that the Vilani Imperium's emphasis on social stability and uniformity allowed to operate well beyond what Terran society would consider the maximum possible span-of-control limit, she was being literal. Terran society couldn't possibly hope to run anything the size of the Vilani Imperium without having the whole thing fall apart in a couple of centuries. Which is precisely why the Second Imperium that was founded when the Confederation finally made the Vilani surrender is noted in history books as "the Ramshackle Empire", and it lasted about as long that name implied.
tldr; The Vilani need a partially decentralized system of government just to
function. If it wasn't for their massive (and
deliberately cultivated) cultural inertia and all the rest of it, they'd already have started fragmenting like the later Roman Empire centuries ago.
In the canon timeline, the Emperor did not personally involve himself in any affair about the Terrans until the year 2229, during the
Eighth Interstellar War. And the only reason it got as high as him is because by that point the Saarpuhi Karshuggi's boss, the
Apkallu Kibrat Arban or 'Minister of the Four Quarters',
had to send a direct personal appeal to the Throne for the entire Imperial Core Fleet to be committed to the struggle, because by that point he was in genuine danger of losing control of the Imperial Rim Province. (Terra had 'broken out of the pocket' several wars ago and had been advancing the frontier inward a few worlds at a time).
If you're wondering why none of them ever reported it earlier, note that admitting to the Throne that shit has gone that far out of hand that you actually need this level of reinforcements is basically synonymous with handing in your resignation. Hell, the Third Interstellar War is the first one that got large enough that Kadur Erasharshi had to tell
his boss all about what was going on, and we know how that would have ended for his career even if his lieutenant hadn't knifed him in the back during the endgame so that his failure would be seen as one of execution and not one of policy. (And thus allow that policy another attempt at success.)
And even at as late a date as the Ninth Interstellar War that huge a mismatch of heavy metal that might actually have broken the Confederation... except that at about the same time, Terran science finally cracked the problem of jump-
3, meaning that they could get around 'behind' the advancing Core Fleet and cut off all their lines of supply and retreat. (Remember Sharik Yangila's noting that Terra and Shulgiasu are only 11 parsecs apart in a sraight line, but you have to dog-leg
eighteen jumps around at jump-2 because the stars don't line up right to make it a viable jump-2 route? If you have a jump-3 drive you can make it from Terra to Shulgiasu in
four jumps, and 2 of those jumps are just getting to Nusku!)
And once the Imperium had to surrender the entire Core Fleet then... well, that was it. It took over half a century beyond that point until the Vilani finally surrendered, but once they lost the bulk of their capital fleet and control of the entire Imperial Rim Province with it, and the Terrans could simply cheat the starmap with jump-3 in ways the Vilani couldn't hope to match, it wasn't a case of "if" but of "when".