In 2000 means sometime during the year 2000 (January-December). By 2000 means before January 1, 2000 This number decreased to 500 by 1964 (before 1/1/1964) and continued to decrease but steeply to 250 in 2000 (during 2000). The figure began to decline and had dropped to 200 by 2000 (before 1/1/2000).
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