If it was done from a collected sample during autopsy, it can not be 4 months old.
At any rate, that level, as indicated by the first paper, is at the upper limit of average people admitted to the emergency room "29 randomly selected emergency department patients (19 males and 10 females, aged 19 to 55) whose urine screened positive for benzoylecgonine using fluorescence polarization immunoassay."
Again though, short half-life, if it was 100+ days old I do not see it lasting still. Also, blood does not last long at all outside the human body.