Dr. Baker did not include the specific test that the prosecution wanted to bring in as "new evidence." The judge ruled that since the prosecution knew about Fowler's claim of potential carbon monoxide poisoning, they should have inquired about it before. However, they wouldn't have known about second test since Dr. Baker left it out of the report. He apparently called them last night to let them know.
Anyway, it seems they didn't need it because Dr. Tobin was able to refer to the test result that was initially included, which was the blood sample showing 98% oxygen, which would mean it would be impossible for the carbon monoxide level to be more than 2%. (I think his level was 1.5, but that information was not allowed)
At least that's the way I understood it.