https://github.com/steemit/steem/issues/2028 tells me my problem with potential NAI space buyout was not unfounded. Turns out it is not 1B but more like 45M SMTs (1 digit out of 9 for checksum, 10% reserved, NAI assigned in pairs).
BTW. thank you @zgredek for the link to issues - now I have to read them all 😞 300 scanned so far, 1000 more to go...