I wondered which passenger train has the largest capacity while travelling in a busy double decker double traction Ouigo train (low cost French high speed train), which according to Wikipedia offer 1260 seats.
I guess you can get different answers for inter city trains with compulsory reservation and commuter ones, and for the latter, the official max capacity and the actual one.
EDIT : to make this question more answerable, I now ask only about seat capacity on a train with compulsory reservation (or at least with an enforced limit in the number of passenger). And I like to limit to regularly scheduled service, not in records like these.
This forum post about Indian trains give higher figures, counting "unreserved seats". Are there enforced limits on theses coaches ?
I believe that technical limitations (especially regarding platform length) should make this question answerable.