Ah but clearly there was an issue here. The stand I was using wasn't housing the puck properly for the 38mm watch. I took it off the stand and charged direct and got to 100%. I never had any iproduct, MacBook that hasn't charged to 100%.
Yeah that's a different story. As for Macs not charging to 100%, occasionally normal behavior, per https://support.apple.com/en-us/HT204054
"My battery will not charge to 100%"