[Etheryte]

You could say the same about cryptographic signatures where each party only knows a part of the key, yet those all work fine. You could probably piece together the formula by a sum of some employees and some external suppliers if everyone broke their NDA, but if people keep their word, your factories could just as well see shipments of "Ingredient A" and the worker only knows how much to add to each batch.

[TeMPOraL]

Real life ain't abstract math. You have MSDS 'mulmen mentioned, but I also can't imagine any factory being able to just mix shipments of ingredients "A", "B", "C", etc. without the actual content being documented on purchase orders, OSHA reviews, etc. You may want to operate in secret, but at the very least, the taxman really wants to know if you aren't skimping on your dues, so there should be plenty of relevant documents in circulation.

[creshal]

Since they're operating in Europe it's trivial to split manufacturing into 3+ places that are within an hour drive but also in 3+ distinct jurisdictions that are part of the same free trade zone, so no tax authority can have a full picture either. And you'll never get, say, French and German tax authorities to voluntarily talk to each other.

[pests]

I do recall some episode of "How its made" or similar of a food factory discussing some mix they were doing for a fast food chain, IIRC, that involved "two separate bags of spices, each sourced from a separate supplier for secrecy". That's about the level I'd expect out of such a scheme.

[mulmen]

I wonder how much information leaks through something like Material Safety Data Sheets.