Far as history goes, real authentic personal letters are a source. Letters to Gail became a three volume set. Gail has retained the originals, far as I know. These letters may not be the same as the printed book versions; or all included in the book versions. Questions arise about the names Kirpal Singh, Sudar Singh and Rebazar Tarzs. Which name(s) appeared in the original letters.
I think it key to determine the actual truth. Some references here
http://dlane5.tripod.com/Dec23.html
and here
http://dlane5.tripod.com/eckdirectory.html