Well the PGM enzyme was negative, and the AK enzyme is also found in animals, and 17 out of 20 markers means it could be half the world plus little green men on Mars.
I think it's best all round to simply say it was not Sheila's blood in the silencer and whoever put the blood in it got lucky with the blood group matching Sheila's.
Unfortunately the other COA forensic evidence confirms Bamber is guilty.
Meaning the blood in the silencer is Sheila's. Via back spatter after Bamber shot her twice.
Even David says Sheila was shot in an area of high blood flow & it is Sheila's blood.
Nice try.