Tenor and Contract dates are related, though not identical concepts in Molecule. Both refer to the forward month (or day, or other period) for which a trade is relevant.
Tenor Start and Tenor End are specified on a Trade, and may span multiple periods.
Contract Start and other Contract dates, however, are derived from the Tenor. They are automatically assigned to Trade Legs, Sublegs, and Valuations, and they span only 1 single period.