Here is the official explanation of the alphanumerals used in the simplex killer part of Cooper types 32,32a&32c/Renouf/Martin types 17,17a&17b duplex cancelations in
Indian Post Office Manual 1873; Chapter VIII: Stock; Section II: Stamps and Seals; pp.80-1.

References:
1. Early Indian Cancellations and Postmarks 1852-1884.
Winter Charles Renouf.
The Philatelic Society of India, Lahaur 1919
Chapter VIII: The All-India System of Cancellations, 1873-1884; pp.53-4
2. Early Indian Cancellations.
Jal Manekji Cooper.
Thacker and Company, Limited, Mumbai 1948
Chapter XXII: All India Cancellations 1873–1884: Types 32–35; pp.73-4
3. Billig's Philatelic Handbook (Vol.XXXIX).
HJMR and Company, Hollywood, USA n.d.
Appendix I: Early Indian Cancellations 1855-1884
Chapter VIII: The All-India Series of 1873-84; pp.506-7
4. Numbers in Early Indian Cancellations 1855-1884.
Denys Richard Martin.
Robson Lowe Limited, London, England 1970
Chapter III: All India System 1873-1884, with Punjab Used Abroad; pp.114-5, 122
5. Indian Postal History 1873-1923 Gleanings from Post Office Records.
Ed. Diljit Sinh Virk.
Army Postal Service Association, Ramakrishnapuram 1991
Chapter IV: Postmarks; pp.65-6
Chapter VI: Illustrations of Postmarks; p.101