On the Vietnam veteran statistics page of this website, it says that 4 out of 5 people that claim to be Vietnam combat veterans are lying. This is based on a 1995 Census in which 13 million people claimed to serve in country when only 2 million actually did.

The following claim was found on this website. It has been cut and pasted all over the internet on many blogs.
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1. 1,713,823 of those who served in Vietnam were still alive as of August, 1995 (census figures).
2. During that same census count, the number of Americans falsely claiming to have served in-country was: 9,492,958.
3. As of the current census taken during August, 2000, the surviving U.S. Vietnam Veteran population estimate is: 1,002,511. This is hard to believe, losing nearly 711,000 between ’95 and ’00. That’s 390 per day.
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I cannot confirm this statistic from the Census site or any other legitimate source.
In fact, I don't think there was a census in 1995 since the census is done every ten years since 1890. The 2000 census did not ask where veterans served.

Can anyone provide a link to a legitimate source of this statistic?