Who performed and entered into these new plural marriages from 1890 to 1904? "A few over-zealous individuals" according to the First Presidency statement of 1907; "a few misguided members of the Church," according to the First Presidency statement of 1933; "devoted but misled members of the Church," according to Apostle John A. Widtsoe in 1951; "some high officials of the Church" according to B. H. Roberts's centennial history which later identified them as Apostles John W. Taylor and Matthias F. Cowley who were dropped from the Quorum of the Twelve in 1906 because they were out of harmony with the First Presidency concerning the Manifesto; "a few Church authorities," according to historians Allen and Leonard in 1976; some "diehards" according to historians Arrington and Bitton in 1979; "some who held the sealing power. The most prominent among those was John W. Taylor of the Twelve," according to the Secretary to the First Presidency in 1984.

Sounds like your research is correct that there were still plural marriages performed post-manifesto. That much seems clear. What is muddy is whether they were, in fact, "Church sanctioned". I don't have any concrete evidence as to that, and I'm not sure anybody does, so I have my doubts.