Before the development of the current programming, US Chess events that were dual-rated (ie as both regular and quick rated events) had to be entered into the US Chess crosstable records twice. As a result these events will show up with two different 12 digit Event IDs.
Also, because of how the old programming worked, if the regular-rated event had the lower Event ID (which was usually the case), and if this was your first US Chess rated event, your quick game count is likely to be twice that of your regular game count, because under the procedures for rating games your regular rating would have been used to start you quick rating. This is no longer necessary under current programming, but we do not have the ability to correct several years worth of events from the past, mostly from 2001 through 2004.
If there is an actual duplication of an event, please report it to the US Chess ratings department, firstname.lastname@example.org.