Correction. There appears to be some misunderstanding relating to the DNA found inside the moderator. As it stands at the moment Sheila's LCN DNA was accepted by the COA as not being inside the moderator.
The paint on the knurl end of the moderator could have made at any time before the tragedies.
I have my own theories about the scratch marks.
When a sample was taken from the underside of the mantel piece why did Jones and Cook not see the scratches on the 14th August? They put a yellow label on the mantel piece from where they got a sample. On the 12 th August Jones was given the moderator and was aware of the possibility of red paint being on the moderator. So why on the 14th does he take samples with Cook and fail to notice any scratch marks which so happened to be where the samples were taken from. I can't see how either of them failed to see the scratches. Unless the knife they used slipped and they made the scratches in an attempt to take the samples. Then those same scratches were used in evidence or made to fit the evidence presented in court. It is possible if you look at it from both angles. 
1) The police did see the scratches on the 14th. They took the samples because not only the color matched but because of the scratches.
2) the notion people often had the gun with the moderator attached in the kitchen to have been able to scratch it at a prior time is contrary to testimony of guns being unloaded and cleaned elsewhere. At any rate, the scratches were zigzags thus NOT CONSISTENT with being made by someone walking with the gun and accidentially hitting the wall or the gun lening against something, falling and scratching the wall on the way down. The zig zag pattern is consistent with a fight fro control of the weapon as peopel pulled back and forth. The only other explanation woudl be someone attempoting to make it look like it was made in a struggle as peopel fought back and forth. So it was either intentionally fabricated or it was genuinely cuased by a struggle over control of the weapon. those are the only possibilities. Being caused prior to the murders naturally by an accident is not possible.
3) The Appeal Court said Sheila's DNA may or may not have been inside and there was no need to decide whethe rit was or not. From a factual standpoint it was, the defense expert chose to ignore that enough markers matched to say it was hers. The defense expert also chose to declare the faint DNA profile was a male though scientifically speaking the claim was baseless. The defense needed more than just June's DNA it needed Nevill's because all experts agreed the blood could not have been June's alone. So the imlication was the minor contributpor could have been Nevill because it was male.
The obvious distortion by the defense was a waste of time though because a DNA test of the blood removed is the only way to detemrine for sure whose blood it was. Testing the moderator would not and especially not testing the moderator after it had no blood left. Any DNA found can't have been blood based in such circumstances.