Des,
Here is what the HBW has to offer (obviously treating superciliaris associated to luzoniensis)
"
Taxonomy.
Turdus luzoniensis Kittlitz, 1832 Luzon, Philippines
Race
superciliaris morphologically distinctive; if found to be equally distinctive vocally, may perhaps be better treated as a separate species. Race
parvimaculatus only rather weakly differentiated from nominate;
shemleyi poorly known, and validity has been questioned. Four subspecies currently recognized.
Subspecies and DistributionC. l. luzoniensis (Kittlitz, 1832) - Luzon and Catanduanes, in N Philippines
C. l. parvimaculatus (McGregor, 1910) - Polillo I.
C. l. shemleyi duPont, 1976 - Marinduque
C. l. superciliaris (Bourns & Worcester, 1894) - Masbate, Negros, Panay and Ticao
Descriptive notes.17-18 cm. Male nominate race is bluish-black from head to back and wings and breast, with a white supercilium from over lores to nape, white wing patch, white belly shading rufous on flanks and thighs and up onto rump; tail black, white tips on outer four graduated feathers; bill black, legs pinkish-flesh. Female has olive-brown crown, grey-brown back, pale grey throat. Juvenile apparently undescribed. Race
parvimaculatus similar to nominate, but has darker rump, and smaller white tail tips;
shemleyi also has darker rump, but slightly larger white tail tips than nominate, female has white throat bordered by grey, reduced white in wing;
superciliaris lacks rufous rump and white wing patch, female has white throat bordered by a black band."
Op.cit.: HBW, Lynx Edicions, Volume 10, p. 766
The only information as to juveniles is from the Kennedy, and referring only to the nominate race. "as ♀ but throat whiter. Bill black or dark horn; eye dark brown; legs pinkish flesh."
As far as the plate in the HBW - for the female it shows only the adult nominate. Where the male is black, the female is brown, the brown is brighter on the mantle and crown, the throat is whitish but with fine greyish streakiness that deepens into simply brown on the breast, the frons and lores look to be darker. The outer four or five primaries seem to have a lighter (brighter?) tone of brown than the rest of the flight feathers.
Well, trying to gather the few tendrils of information that we can glean, I suppose we can only conjecture. The juveniles of all of these races apparently start out with a whiter throat than the adult (exception made for adult female shemleyi, and superciliaris, that remain white). I can't make any guesses about the ill-differentiated parvimaculatus (though I might expect the female to be similar to the nominate given the close approximation of Polillo to Luzon). As for the superciliaris, the juveniles and the adult females have whitish throats apparently, and I would expect the subadult males to transition directly to black on the throat without intervening gradations of other colors. The mantle of the female superciliaris is definitely dark (not brown as in the nominate, and possibly? parvimaculatus). It appears black. However, guessing again, I would expect parts of the adult female to be duller than the adult male, and I think we are seeing some of those features here, cf. the crown color, the outer primary color, that probably remain dark brown, duller, and not black as in the male.
I agree that the bird in the photo is certainly not a juvenile, well, since this term is so undefined, not an early juvenile - the juvenile flange has been completely reabsorbed and the bill is deep black. Nonetheless, certain immature features seem to persist - notably the non-cleanness of the black pectoral (still splotchy) and the slight indications of a persisting - almost certainly juvenile rufousness of the breast below the pectoral band. Des, I think you nailed it by saying that this is subadult! We can't call it a full adult, but we are almost there...
audiofiles (superciliaris):
avocet.zoology.msu.edu/recordings/10663www.xeno-canto.org/asia/browse.php?query=White-browed+Shama+%28Copsychus+luzoniensis%29+11&species_nr= Only Tracks 1, 4, 9 and 10.
