I believe that the adding in of the 4 bullet cases into the main bedroom scenario, for the purpose of bolstering up the prosecutions case, so that it could be argued that Sheila had been shot twice in the bedroom, and that Neville had been shot 4 times upstairs in the bedroom, has actually worked detrimentally, undermining that narrative, since if June got shot 7 times and Sheila was shot twice in the main bedroom, then Neville could not have been shot 4 times in the bedroom, because of the existence of a spent a case outside the main bedroom door and on the top landing.
Similarly, if Neville had been shot 4 times in the main bedroom and June had been shot 7 times, then Sheila couldn't have been shot twice in the same bedroom, because of the existence the 13th spent bullet case outside the main bedroom on the top landing...