About only the latest submission being valid: I think it would be more interesting if each team could submit a handful of submissions (three or five). That fosters more daring explorations, since at least one of the submissions can be really risky. It also allows making mandatory, for example, that one of the submissions uses only the provided data.
In any case, I’d like you to clarify what constitutes a “team”, because last year we had different user accounts with essentially (or exactly) the same team composition with different submissions. Will this be allowed for everyone? To which extent?