I can't necessarily speak to the "quality" per se, but I have done some reading into the traditional use and modern misuse of coca and might be able to answer your question. As cocaine is just an alkaloid present in the coca plant, it has to be extracted somehow. When cocaine became popular again in the 80s, the process for its extraction had already been developed in the late 1800s. The main solvent used was acetone (nail polish remover), which may sound unhealthy but pharmaceutical cocaine is still produced with this method. After you extract the cocaine alkaloid, there's various methods of converting it into a salt, washing the chemicals off and finally drying it into a powder. The main thing that's changed since the 80s is the solvent and other chemicals. Acetone is expensive, unleaded gasoline is not, and both are non-polar solvents.

Effectively, as cocaine production boomed and landed on the radar of law enforcement, it became much more difficult for narcos to aquire industrial quantities of things like acetone. So while on a molecular level the process is effectively the same, the chemicals used are very different. Additionally, as cocaine production exploded, the chemists were followed by workers who began simply following a recipe. This meant that steps necessary to chemically wash the cocaine were not necessarily done correctly. All of these factors have led to cocaine today having all manner of chemicals and byproducts left in it that cocaine produced in the 80s might not have. I have heard that good cocaine "smells and burns like gas" in your nose and my guess is that is because there is still minute quantities of gas in it.

I hope I've answered your question, or at least given you an idea on the history of cocaine production and how quality may have changed temporally. I'm also not a user of cocaine so I don't really know what you mean by "quality" but I am somewhat familiar with coca and its traditional and untraditional uses, illicit or otherwise.