Finally, after 1 year and 2 months of struggle, I could convince SER/ECR to de-reserve one coach of 2S :)
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"In the context to your CPGRAMS complaint dated xxxxxx, it is hereby informed that One (01) unreserved coach with 2nd class Mail/Express fare shall run for journey commencing ex. Hatia and Islampur on and from 01/12/2021 for Train nos 18624/18623 Hatia-Islampur-Hatia Express."...
more...
First, they asked me to go for advance reservation in 2S, as the CURRENT BOOKING funda does not work in this train between PNBE and IPR.
BTW, this they have done, just after I asked for the revenue and earnings of this train between IPR and PNBE and vice versa.