I am running 10.0, SP5 and attempting to merge 12 point shapefiles. Each file contains AIS data for one month of the year. The merge completes successfully but the dates in my date field become corrupt. The date for most records will become modified and either be blank, change to "12:00 am" or become some other date, e.g. 12/21/7200. When I merge 2 or 3 together no change occurs. But, if I add a fourth or more, the dates modify. Any idea why? The number of points in each file ranges from approx. 886,000 to approx. 1,290,000.