Do you have a source for this? Because it doesn't sound right to me. And also, I live in a coffee producing company, work adjacent to the coffee industry, and had a long conversation with someone planning to set up a business exporting green beans to the US, and their beans were getting tested to an extreme degree and being rejected for a few ppm over on certain things.
I have heard the 3% rule but fyi it's 1% in the EU and since there's actually not that many large scale decaffeination factories in the world, as far as I know they all target the EU level.
If you buy small batch, large batch, or somewhere in between it's probably been processed in one of these few large factories.
https://www.sciencedaily.com/releases/2006/10/061012185602.h...
And that article links back to this UFL press release. I've clicked every link I can find and there's not an actual, published study to be found anywhere:
https://archive.news.ufl.edu/articles/2006/10/uf-experts-dec...
But even if there was, is a study from 20 years ago still relevant?