> Several big cups of decaf can approach the caffeine content of one regular cup

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.