Thanks for the identification of original Image posted by me Dr Seow.

Even I am interested in the question of our good friend Rajib.

Let us assume we have UP view along with UN view also.
How can we differentiate between the three species? P. mathias, P. agna, P.thrax.
Broad guidelines also sufficient now.

No. We do not have P. thrax in South India.

Synoptic Catalogue (Varshney and Smetacek) says

221. Pelopidas thrax (Huebner, [1821]) Small Branded Swift
i. Pelopidas thrax masta Evans, 1949
Sikkim to N.E. India.
ii. Pelopidas thrax thrax (Huebner, [1821])
Jammu & Kashmir to Delhi & Gujarat.

We have heard of reported presence of Pelopidas thrax masta occurence in West Bengal, but it is not confirmed by voucher copy and genitalia studies. Hence we do not have confirmation as of now. The reports are based on images. So we would like to understand pictorial id first before more evidence can be found.