If $Q_k$ is derived from another method but shares the column space of $F_{n,k-1}$ then there is still mathematical equivalence between methods 2 and 3.
If one minimizes with respect to a different norm then the methods correspond to other methods discussed here.
\node[align=left] (preBroyden) {$\begin{bmatrix}\vec{1}^\top&\vec{1}^\top\\ F_{n,k}& B \end{bmatrix}\vec{u}=\begin{bmatrix}1\\0\end{bmatrix}$,\\$\begin{bmatrix} X_{n,k}& C \end{bmatrix}\vec{u}=\hat{\vec{x}}$};