If you create an on demand report for "Chart per Metric with Multiple Items" and have devices with different number of samples.
In versions prior to 2.7 there is a single listing of number of samples/resolution at the top of the CSV even though the number of samples may be different per item
Performance Management 2.7 and later
An enhancement has been made to improve the clarity of the CSV view exports.
In 2.8 there is an individual resolution/number of samples per item for every item