Russell's theology did not derive from the Millerite movement. He was introduced to Literalist prophetic interpretation by his congregationalist pastor. He examied Adventist teaching, rejecting it in favor of American Literalism, and from 1871 to 1876 he identified with the One Faith movement, not with Millerite Adventism.
The One Faith movement were age-to-come believers. Stetson adopted that theology in 1863, though he remained within the Second Advent communion until his death. Storrs left Millerite Adventism in 1844, and there was constant tension between him and Adventists.
Various age to come and One Faith congregations are often called Age to Come Adventists. They rejected the identity, but sought cooperation with Advent Christians and others. A push to remove age to come believers from AC congregations came to a head in 1874-1878.
Russell was never an Adventist. He was a Millennarian. The Millennarian movement did not derive from the Adventist movement, but preceded it, and was the mainstream in the US and UK. It is nonsense to suggest Russell's theology derived from Adventism. It's unhistorical.
More on this is on the private blog.