I sat in on a discussion with Darcy on Clubhouse, yesterday, and came away with more questions than answers.
At the moment, it seems to me that Darcy is talking about American chemist/pharmacy/soda fountain recipes—his specialty—for what is either ersatz pomegranate syrup, and/or a floral/clove syrup that is both linguistically entangled (grenadine/grenadin) and flavor-entangled (he has made a batch and says there are taste similarities). Darcy conjectures that bartenders probably purchased such things from pharmacies for use in their bars.
To me, this all seems entangled with the copious ersatz ingredient recipes (e.g., for compounding ‘rum’ or ‘brandy’) that we have in various professional manuals throughout the late 19th Century, but with little evidence—to my knowledge—of how often these ersatz recipes were actually employed by bartenders in place of the real things. (I can speculate that the finer, more expensive bars had the real stuff, and that ‘anything goes’ at the cheap saloons, but that’s perhaps simplistic.)
Then, there’s the international question raised by @francois, complicated by a huge fraction of grenadine drinks emanating from European bars, rather than American. And the problem that @Splificator has already documented a marketplace of the commercial, artificial grenadines we know and loathe by… the 1890s(?)… that may not have even been driven by the ‘American Bar’ at that point, since grenadine in mixed drinks don’t seem to proliferate until later?
Anyway, this is fun!