Can't say as for the USA, but there's been some reports based on drugs seized in Europe from the 90s to pretty much nowadays, and the results are that drugs have steadily become more pure and with less dangerous cutting agents. With the exception of 2008-2009 global "drought" when China pulled the trigger on the export of precursors, when MDMA prices spiked wildly, bringing up the consumption of MMC and MDMC, prices and purity of MDMA are down and up, respectively.
I don't honestly know who would know from the 80's though.