I’ve never actually had an older Bacardi, but I did just translate a fascinating chapter of Kervegant’s text (1946) where he describes the rums of the world. Cuban rums of the 1930’s were known for distillation parameters, and then filtration, that would make them fairly neutral no matter the potential of the ferment. The rums were also known to be adulterated and probably very skillfully.
When I recently corresponded with one of the top Cuban rum researchers, he was not aware of Arroyo’s works, and one of their recent published papers was on a new method for artificial aging.
A problem with part of the chapter is that pretty much all knowledge of quite a few of the rums comes only from a large 1937 IRS survey. Kervegant certainly knew the rums of Martinique and Guadeloupe, but likely never tasted any of the others.
Elsewhere, Kervegant mentions a trend at the time (since the beginning of the 20th century) to dramatically speed up fermentations. There are no real fermentation additives we have now that they didn’t have them. They even had antiseptics. We seem to have lost a lot of information since then and gained very little.
The big thing that used to be more common that the industry seems to have lost all knowledge of is Schizosaccharomyces Pombe ferments and the use of symbiotic bacteria. We are nearly 80 years after the work of Arroyo and no one can do it outside of Jamaica.