Rodger,

IMHO your hypothesis is spot on.

Donald Ross disbanded Northern Evangelistic Society in Aug 1871 and started to break bread according to NT simplicity independently of any involvement from OB or EBs (according to Ritchie).

Donald Munro visited Canada for the first time in September 1871. There was a letter from Munro giving an account of his journey in the Nov 1871 ed of The Northern Intelligencer.

During his Canada trip Munro examined the word of God and was convinced on the position of Believers Baptism ( Ross who had got baptized in April 1871 had written to Munro about his excercise of soul about baptism).

After two months stay in Canada , Munro came back to Scotland in Nov 1871 & was baptized by Ross on 31/12/1871.

In 1872 October, Munro went back to Canada.

Ross was in fellowship with the OB as early as Jan 1873. The Jan 1873 Northern Intelligencer has an address by OB preacher from Glasgow, Mr Alexander Stewart. There are links to H Groves from May 1873 Northern Assemblies.

( It is possible that this fellowship may have happened 3 months earlier when Munro was still in Scotland. I haven't come across any reference for this and I could be wrong. Even if it happened only after Munro left for Canada, it is extremely unlikely Donald Munro was unaware of this coming together while staying in N America as both Ross and Munro kept each other informed of happenings on both sides of the Atlantic).

Munro came back to Scotland in June 1876 and by the end of the year Ross accompanied him to the America.

While Mr Ross & his friends' separation from Presbyterianism & subsequent understanding of Church truth and gathering of believers may have happened  independently of so called Brethren, Ross & his co-workers came into fellowship with the Open brethren in Scotland before the start of GHBs in America.

So while GHBs may not be directly connected to original OBs of Bristol and Devon , they are connected to OB by the fellowship of Donald Ross to OBs.

Norman Crawford's premise that they don't have any historical connections is not reliable .