I count 21 on the MT starburst...
I count 21 sectors on the map that are outside the Solomani Sphere and likely are duchies...
SM
| Den | Cor | Vla | Lis | Ant | TEQ |
(tr)
| (Ref) | Gus | Dag | Cor | For | Ley |
| Ver | Ill | Zar | Mas | Del | (GR) |
| (Eal) | ReD | Daib | Dias | OExp | (Hin) |
| | (DN) | (Mag) | (SolR) | (AlpC) | |
Parenths indicate probably not a duchy until after the 990's...
Dark Neb and Ealiyasiyw are probably combined with Reaver's deep.
Trojan Reach is canonically run from the Marches.
Reft is run from Deneb in the spinward, and Gushemege in the trailing.
Magyar, Solomani Rim, and Alpha Crucis are all deep inside the Solomani Sphere until after the Rim War. At which point, the Solomani Rim likely becomes a sector government, and the small chunks of non-solomani Mag and AC probably fall to it.
Hinterworlds is canonically out of Old Expanses.
Glimmerdrift Reaches is probably split between Delphi (rimward/spinward) and Ley (Trailing coreward).
Canonically, most of the 3I is stabilized by 200... (Thanks to T4 sources...)