Juniper berries can conceal a multitude of sins.

During Prohibition, there was a thriving industry in "renaturing" industrial alcohol that had intentionally been made unfit for human consumption.

Cocktail historian David Wondrich probably has a great deal more to say on the subject, but he's cited in this Old Tom gin article as saying:

...fundamentally driven by the fact that before the introduction of the column still, capable of producing very pure “neutral” spirit, the base alcohol for early gins would have been crude and distinctly flavoured—indeed much of the botanical flavouring might have been there simply to try and make the spirit more palatable, as might any sweetening or deliberate ageing in wood (something which lies at the heart of whisky making).

This isn't a top-level reply and I will delete it if asked, but as a follow up, I have heard that the term "gin" was much less defined a hundred years ago. Juniper was present but the typical juniper/citrus/coriander makeup that we see now is a recent standardization. Can anyone elaborate on this? I'm not referring to sloe gin or Dutch Genever either. If memory serves, any rot-gut someone made and put juniper in was a gin, however palatable it may have been.