[DL-Invariant]

You're correct in your baseline of thinking. If you dig into the valuation portion of the article, I explore that a bit.

International growth, strong USD, usage rates increasing. Overall, it's volumes vs inflation. Volumes have been growing faster on a relative basis.

Certainly a long-term risk; just one of many.

[jsmith99]

Additionally, the driver for the huge volume increase was partly Listerine going down market from an expensive medicine to a mass market product. $20 in 1881 is apparently equivalent to $580 now. J&J probably only get around $200 revenue for each gross of Listerine sold now (a guess based on retail prices and markups), suggesting that despite inflation the royalty is still a respectable 10% but implying the 1881 price must have been much higher, in real terms, than Listerine costs now.