I have the The New Green Mountain Songster. Flanders reprinted Cahrley's Escape twice but I wasn't aware that it was online.
GMS was compiled by a Revolutionary War veteran from Sandusky, VT, which possibly dates back to the 1700s.
The GMS is apparently housed at Baker Memorial Library in Hanover NH. Some of the texts have been published - not sure why the whole book is not available.
This is another example of an important book not available to the public. The same thing is true for many of the collections at LOC and US libraries. There's no money and no intiative to have the collected material made public (online).
Here's GMS version on my site: