It looks to me as if it would be easier to avoid strange results if you left out the EndDate column. Since you say tha entering a start date in the past or in the future is not allowed to happen, the end date is redundant and can only add scope for constructing inconsistent data.

edit: some queries will be a little more complex without the end date column. This is a small price to pay for the reduction in complexity of inserts (and of updates and deletes, if there are any).