true, and indeed why I often say "INR is not like measuring a piece of steel"
Medicine is actually more like an art than a science, it does however lean heavily on science (such as molecular biology), but the whole system of our body is very complex and we often have no idea why something works (like paracetamol). The pharmacy industry is filled with examples like amiodarone
Amiodarone was first made in 1961 and came into medical use in 1962 for chest pain believed to be related to the heart. It was pulled from the market in 1967 due to side effects. In 1974 it was found to be useful for arrhythmias and reintroduced. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. In 2020, it was the 198th most commonly prescribed medication in the United States, with more than 2 million prescriptions.
or medicines that were developed for one thing, then found a use in another area entirely. Usually all by trial and error.
I would however say that there are "best practices" but these are often also about psychology (like using a pill box because its more than just a convenience).
All these things should be sets of systems designed to prevent accidents ... like a safety net. They are not the word of God because God never gave us his word (ask a Christian (pick your heretic flavour) or a Jew or an Islamic for what that word is) and usually evolving. So its good to keep up with what is best practice now.
Like medicine most people don't actually care about precision and some people care enough to try to guide the others.