Indian casualties are also not very prominent/clear in the statistics. In Appendix 17 of Maurice's Vol 4 History, he lists the imperial units, Militia, IY, CIV etc and then the Australian, Canadian, NZ and SA contingents. Before the final category of surgeons and civilian in military employment, he has 'other Contingents' which total 33 of all casualty types.
I was very surprised to read that your proposed contribution was turned down. If the conference was being held in the old South Africa in the Orange Free State, where Indians were unwelcome, it might have been understandable. It would be interesting to know the reason.