Poorabiya Express: कोसी की शान से दिल्ली महान तक - Md Rashid Alam

This is the opening day Quota of this train checked by me today before 8.00 AM -
GN Quota - 195
POOLED Quota - 18
LOWER BERTH Quota - 10
TATKAL - 80
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Quota - 18
So total Berths comes to 321.
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Coach composition of this train shows 4 coach of 3AC, where as total available berths are 1 berth more than 5 coaches. So actually how many coaches are there in this train (yet RAC seats are not included) ?
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As shown that this train have RSA with 12631 Nellai Express, which have 5 Coaches as per CC, but how come one extra berth of total coach strength ?