Iterations are a hierarchy. Within a single team you wouldn't have overlapping iteration dates, but if you have multiple teams within a team project you can model it as a hierarchy of iterations. Something like so:
Team A
Sprint 1
Sprint 2
Sprint 3
Team B
Sprint 1
Sprint 2
Sprint 3
Then in the team settings you just have to make sure to only associate each team to the iterations for that team. So long as no iterations assigned to a specific team overlap you should be OK.