If I understand the report correctly, there were blood tests carried out at the time of the Post Mortem which indicated the blood was well over the normal levels, ie he was drunk.
Allegations since then have suggested that the blood was swapped in an effort by conspiracists to cover there tracks... in other words, the original test on the blood was falsified.
This recent test, performed within the last year, is a DNA test on the blood sample that was used, which shows that the blood is in fact that of the driver..... not a simple blood alcohol test.
As to why this wasnt done at the time.. who knows? Maybe given the state of DNA testing at the time, or the amount of blood sample available or whatever, they weren't able to perform the test.