Mad Cow Test: for seven months there was no bad intention or cover-up, and the test in question was only experimental.

For Months, Agriculture Department Delayed Announcing Result of Mad Cow Test - New York Times: "By DONALD G. McNEIL Jr. and ALEXEI BARRIONUEVO | Published: June 26, 2005

Although the Agriculture Department confirmed Friday that a cow that died last year was infected with mad cow disease, a test the agency conducted seven months ago indicated that the animal had the disease. The result was never publicly disclosed."
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For seven months, all that was known was that a test on the same cow done at the same laboratory at roughly the same time had come up negative. The negative result was obtained using a test that the Agriculture Department refers to as its "gold standard."

The explanation that the department gave late Friday, when the positive test result came to light, was that there was no bad intention or cover-up, and that the test in question was only experimental.

"The laboratory folks just never mentioned it to anyone higher up," said Ed Loyd, an Agriculture Department spokesman. "They didn't know if it was valid or not, so they didn't report it."