Over on the International Tax Blog, it was reported that 1997 had more Americans renouncing their citizenship than in 2011 (1,812 versus 1,781). I was very skeptical of this number and it was Tim who finally gave me the information needed to solve this riddle. He linked to a GOA report that mentioned in passing what happened. First, the IRS keeps a CLN (Certificate of Loss of Nationality) database. (that would be an interesting FOI request). 1994 was the last year the IRS was tracking CLNs by year. By the time they were required to track this again (the 1996 HIPAA law), they couldn’t distinguish the data from 1995, 1996 and 1997. The GAO report states that they reported these renunciations in a group.
Thus, each of those three years had, on average, 604 renunciations, making 2011 the largest number of American renunciations in history. As you can see from the graph below, the numbers now look “correct” and there is, indeed, a sharp upswing in the number of Americans renouncing their citizenship.
I have expanded a bit on this explanation at the Overseas Exile blog.