I also heard that rumor. Unfortunately there seems to be no documentation as to what information and where it went in our dancing. What is documented to some extent is that all of the dances in the first three books, were already in print and circulating outside the society. The difference being that our first books, were also the bulletin and hand book, so we were able to put our stamp on what followed. Where it specificly came from before book one is anyone´s guess. As to the later dances they were simply reconstructed from dance books found in libraries and private collections.
The problem with RSCDS footnotes, as it used to say if one read the fine print, is that they are not footnotes, only the earliest known reference to a dance of that name, but not specificly the dance that we published.
As to Miss M´s pre Book I expertise, note that in the famous precurser, the Beltain Society (reference to McFadzean´s "house" bio of Miss M, all of the dances performed were already revived by the EFDSS and are still part of their rep.
It was not until several books into our series that we invented something called "Scottish Country Dancing", our original definition was "country dances as danced in Scotland". Miss M, and the society, created a border between the country dancing of Scotland and England, that had not existed previously. Even most of the Scottish music that we now use, was first published in London (majority of Gow, Bremner, etc.). In the various sources, most of the dancing masters came from the south or the continent. When it comes to a lot of the Highland material, its source can be traced back to Belgium.