For me, recreating or even just approximating pre-ban absinthe characteristics isn't about religiously following a set of formulas and processes from Duplais. It's about doing what it takes to get that flavor.
I couldn't agree more. That's the approach I used to develop L'Ancienne, successfully or not it's not my place to say.
I think chemistry is important, but not THAT important. Something can look like a perfect copy of [insert pre-ban brand] on the GCMS paper, and yet it tastes different. There are too many variables when it comes to flavor and aroma to rely on a formula, or a scientific paper. Recipes, lab analysis, etc, can be good starting points, example: I found a specific kind of fennel that shows a really interesting GCMS makeup, I think it would be a good idea to try it, but in the end it's all about if it tastes good in the absinthe or not. If it doesn't, no matter how similar it is to the fennel used in pre-ban absinthe I'm not gonna use it.
I think it would be naive in the extreme to think that Duplais' dozen or so recipes are a comprehensive representation of the scope of pre-ban formulas. This is not to say that Duplais isn't an invaluable resource for understanding absinthe production and formulation, only that Duplais couldn't record everything: there were literally hundreds, if not thousands, of other ideas and formulas that are now lost to us.
Most (honest) absinthe makers, pro and HG, will readily admit that when they first started making absinthe, they discovered certain aspects of Duplais' recipes—coloration for example—that simply had to be adjusted; sometimes by as much as 90%. Does that mean we're cutting back? I suppose it might, but I don't think it means we're compromising either authenticity or quality.
I would actually go as far as to say that the recipes and protocols described in the Duplais, Brevans, etc, are nothing more than a guideline, and pretty much everything has to be adjusted. This doesn't make them any less important, if it weren't for these manuals (and the tradition still alive in Pontarlier) we would have no idea about where to start about making absinthe. I have an old Italian liquor-making manual from 1920 and in the section dedicated to vermouth production, the author explicitly states that the recipes and protocols that follow are just guidelines, and not to expect to be able, following those recipes, to recreate something that tastes like the best vermouths on the market. He then openly suggests to use them as a starting point, and then modify them according to personal taste, or clients' taste.