Serial numbers are supposed to be unique. The Bureau of Engraving and Printing accidentally printed duplicate serial numbers for some $1 series 2013 star notes. The range of serial numbers that were duplicated are as follows:

B 0000 0001 * - B 0025 0000 *
B 0320 0001 * - B 0640 0000 *
B 0640 0001 * - B 0960 0000 *

In late 2014, the Bureau of Engraving and Printing (Washington DC facility) printed three star note runs for the New York "B" district. Nothing special about it. They printed these serial number ranges:

Printed in Washington DC
B 0000 0001 * - B 0025 0000 * (October 2014)
B 0320 0001 * - B 0640 0000 * (November 2014)
B 0640 0001 * - B 0960 0000 * (November 2014)

A year and a half later, the Bureau of Engraving and Printing (this time the Fort Worth facility) printed three more star note runs for the New York "B" district. They printed these serial number ranges:

Printed In Fort Worth
B 0000 0001 * - B 0320 0000 * (June 2016)
B 0320 0001 * - B 0640 0000 * (June 2016)
B 0640 0001 * - B 0960 0000 * (July 2016)

As you can see, there are a lot of overlapping numbers. This is never supposed to happen, and why you might've seen a message like Multiple Matching Runs Found in your Star Note Lookup results.