These Hawkmoths can be very confusing.
The more you look at them the more you suspect it is a different species.
I am reasonably confident most of the IDs are correct except perhaps no. 14.

I thought I'll put them in a key that can compare their features easier.
I follow Holloway in using the term postmedial, medial & antemedial.
Medial refers to any markings in the medial zone , the central zone around the discal spot.
Postmedial is any markings in the postmedial zone ie just outside of the medial zone.
Antemedial is any markingd in the antemedial zone just inside of the medial zone.
In Acosmeryx it is the postmedial which is prominent and dark.


A. FW without a defined triangular costal patch, the pale region continues to the outer margin.The postmedial runs obliquely to the tornus.

1A. pseudonaga ; Dark & contrasted ,the postmedial curved , the outer margin slightly angled.An inner narrow arm may be weakly present. Wing margins smooth.
https://www.flickr.com/photos/jatishwor/15770858880/

2. A. shervillii
Similarly marked to A. pseudonaga, the ground paler only the postmedial dark.
https://www.flickr.com/photos/gancw1/3909344279/

WEbsite contain both A. shervillii & A pseudonaga (then still combined as one species).
https://tpittaway.tripod.com/china/a_shv.htm

3. A. sericeus. FW postmedial bifurcate into two arms of equal darkness. Markings more contrasted with whitish edgings; Wing margins crenulate, with slight irregular undulations.
https://tpittaway.tripod.com/china/a_sri.htm

4. A. sinjaevi FW with a straight postmedial running from costa to just above the tornus.
https://tpittaway.tripod.com/china/a_sin.htm


B. FW with a pale costal triangle sharply defined. Postmedial outer arm is strongly angulated.

5. A. anceus.The two arms of the postmedial enclosed a quadrate space; FW with a prominent mid-margin angulation.
https://tpittaway.tripod.com/china/a_sud.htm

6. [I]A castanea./I] Similar to A. anceus but the inner arm of the postmedial is obsolete . FW margin smooth ,without a mid-margin angulation.
https://tpittaway.tripod.com/china/a_cas.htm


C. FW with less defined costal triangle with pale shading connecting it to the outer margin.

7. A. omissa. Postmedial is curved angled on the outer side & sharply defined on the inner side. Wing margins crenulate.
https://tpittaway.tripod.com/china/a_omi.htm

8. A. pseudomissa.Similar to A. omissa with the postmedial smoothly defined on the inner border. Wing margins entire, not crenulate.
https://tpittaway.tripod.com/china/a_pse.htm


TL Seow: Cheers.
Correction ;No. 14 is Acosmeryx pseudonaga The wing margins are smooth, not crenulate.
15 is correctly A. sericeus.