Sometimes a case that is current one month will not be current the next month.  This occurs when the annual numerical limit has been reached.  This usually happens near the end of a fiscal year (October 1 to September 30 of the next year).  When the new fiscal year begins, the Visa Office gets a new supply of visa numbers and usually brings back the cut-off dates to where they were before retrogression.

Source: U.S. Department of State.