Am I reading it wrong? The chart makes it look like Amex has 23%.

I'm referring to the cards in circulation number. The original claim was about a percentage of consumers, not a percentage of transactions so to me that is the more relevant number.

Either way, 100% - 23% = 77% which is > than 70% so the point stands. Visa + Mastercard alone are over 70% using the purchase volume numbers

Yeah, when Google said "over 70%", I basically just figured "Okay, so they have Mastercard and Visa." Amex and Discover are both tiny comparatively.

Which means that 70% is possible without AmEx?

I'd also wonder about how the numbers are computed - you can get incomplete records on a high percentage of consumers without the AmEx data as (people with AmEx) and (people with other card(s)) aren't disjoint sets.