get_session_statistics

LIS's own bill counts for a session, by chamber of origin and legislation type.

One row per chamber and type (B bill, J joint resolution, R resolution); a type with no bills has no row. total is introduced plus continued_from_last_session, and passed counts chaptered plus vetoed bills. LIS computes these counts itself and they do not always agree with the bill list: a total can miss by a bill, the outcome columns add up differently in each session, passed_house and passed_senate are not a funnel, and continued_to_next_session overcounts (pending matches the next session). Count from list_bills when a number has to be exact.