Hi David, I have also worked for frog so it’s a bit of a small world. Hartmut Esslinger, Don Norman, and Ulm School of Design are definitely all interesting additions from the frame of emotional design. I’m still not 100% sure how they fit, but you are right they do.
The 90’s are IDEO heavy — no I this isn’t an adventure for them — however you have to be honest they are also the most prolific during that period for publishing books, appearing in articles and sharing tools for that period. They taught at universities, founded d.School and created method cards. I feel like they really popularised the approach. That doesn’t mean in any way that the approaches they where using were exclusively theirs. In fact I hope to make it clear design appropriated most of those from social sciences.
I am quite sure many design agencies and individual designers have been applying forms of design thinking concurrently or even prior to them however they have not been as open in sharing their opinions, tools and discoveries. Frog does deserve a shout out though they did create a great toolkit for called the Collective Action toolkit human centred design in 2012! And has since started teaching Design thinking methods on Lynda.
Smart is equally worth mentioning, although they haven’t released many tools for public use, they do have fantastic case studies like the OXO Good grips swoon and I over anything Femme Den.