So I have found documents that say the tests were done on one single flake of blood . That is all
So as we are all so unbiased - lets consider JB is innocent
What could have happened
1) There was no test to establish it was back splatter - documented
2) There was one single flake - tested - documented
3) It could have been contaminated by the family
4) it could have been contaminated at the lab
5) it was never human blood.
6) the blood flake was not tested correctly.
7)the tests were misinterpreted
the tests were done after a firing of the rifle and the blood was pushed into the silencer whilst in the lab
Let me make it clear I am not saying any of the above did happen - but keep this in mind because in the future this may have to be explained if it is proven that JB is innocent 
I am being objective and rational while you are not.
There is no such thing as a test to determine if a single drop of blood is drawback. Such has to be evaluated based on the TOTALITY of the circumstances:
A) was there a contact wound that would result in drawback
B) was it found more than 5mm deep but not deeper int he weapon than drawback could account for
C) was there other blood in there and how was it distributed.
You want to ignore the other blood removed by the prosecution and defense that was human group A blood because the only way such blood could have gotten in the moderator was drawback and it thus goes against what you want to contend. The volume of blood on each successive baffle decreasing is what would result from blood being sprayed inside.
There is no way the family could have innocently deposited blood on the first 8 baffles with it reducing as it gets deeper inside. There is no way to take blood from a dried stain and to transfer a flake into the moderator period let alone to do so by an innocent accident.
If blood is wet in a barrel then firing the gun can result in some being removed though not all would be removed. When blood dries the grooves of a barrel shooting the gun alone will not extricate it all from the grooves let alone will the bullet propel it out.
The only way for blood to have been planted would be by someone who knows all about drawback and how to mimmick it including finding a device to spray blood inside so that it deposited on the first 8 baffles and did so in a manner that the volume on each successive baffle decreased. The only people with such expertise were in the lab and only they had access to Sheila's blood type. The family didn't know her blood type nor did police initially.
That is why the defense was unable to make ANY arguments to the courts OTHER than to suggest that the blood inside was Nevill and June's blood that got there from drawback.