I got it right and skipped past E not because it could be SARGable, but because the index is keyed to StartDate and that IS SARGable, and I figured that the system would seek out the rows based upon that and then "scan" the index for EndDate, even if it has to look at all values in the index that meet the start date requirement (but still technically a seek). I will be curious to see how the ISNULL can be SARGable as well.