No. But since you’ve been reticent for some reason to divulge what you know and haven’t given any links, you have given us nothing to rely on.
For the rest of us, I found some different things. One, substances that are present in the corpse may not have been ingested and could be due to decomposition and substances that were present may not be detectable or it may be impossible to determine that they caused the death:
“Post-mortem changes render the assumptions of clinical pharmacology largely invalid, and make the interpretation of concentrations measured in post-mortem samples difficult or impossible. Qualitative tests can show the presence of substances that were not present in life, and can fail to detect substances that led to death. Quantitative analysis is subject to error in itself, and because post-mortem concentrations vary in largely unpredictable ways with the site and time of sampling, as a result of the phenomenon of post-mortem redistribution. Consequently, compilations of ‘lethal concentrations’ are misleading.”
Post-mortem clinical pharmacology
This research paper likewise shows the difficulty of determining levels present at death:
Abstract: Multiple interacting factors alter the measured concentration of almost all drugs after death. The ratio of centrally to peripherally collected samples provides an indication of this redistribution. At present, there are no reliable markers from which to accurately predict how much an individual drug has redistributed. Knowledge of antemortem factors is essential for the interpretation of the effects of any measured drug or toxin.
The concentrations of most drugs alter after death as a result of numerous mechanisms. These and other factors identified as changing the concentration of a drug postmortem are presented in
Table 1.
[Full text] Interpreting postmortem drug analysis and redistribution in determinin | PLMI
This article appears to state that the amount of opioid in the body may be able to determined. But I think they’re talking about fresh corpses. Someone take a look and tell me.
Toxicologic assessments in acute heroin fatalities. - PubMed - NCBI
All in all it looks like the presence of opioids in the body may be able to be detected in hair follicles or in body tissue. Maybe even at the two week mark. But whether this caused death seems to be an impossible determination in a corpse that has decomposed for that long. It’s hard even in corpses where the person died recently.