And the source of the analysis of the "myth" is Chatham House, an "independent" organization led by two ex British prime ministers and one ex MI5 member.

Just look at the list of the Chatham House Prize winners [1] and try to find one person there that is not anti russian.

I guess one could find State Department press releases less biased than this organization.

[1] https://en.wikipedia.org/wiki/Chatham_House#Chatham_House_Pr...

Even your link does not say what you say.

It says US secretary of state James Baker told Gorbachev NATO forces would not move east from Germany. Then it goes into that there is a lack of formal, legal enforcement of these promises, and how the US changed its mind later. So even this source with its leanings does not say what you say.