My guess is, for the Bolt at least, that they did not really have much buffer in the battery (5% or less), and they claimed charging to 100% everyday was OK. Tesla also supposedly does not have much of a buffer, but they have always recommended charging to 90% everyday, 100% for trips. Ford also has 70% warranty, and they recommend 90% charge limit, even though they do have a big buffer (10%). I believe Etron also has a big buffer. When a manufacturer leaves a big buffer, they can always give you back some range on your car with a software change later on if it degrades below the warranty.
I think the Hummer may have a 5-10% buffer at the top, but I personally will likely only charge to 80%, which is what I do in my Mach E. After the Bolt battery fire issues, I normally only charge it to 88% now, that is the hilltop reserve setting. I used to always charge mine to 100%.