Bookkeeping is like working on a loom, weaving with yarn. Each strand of yarn is like the running balance in each account in the chart of accounts.
It makes sense to think of the OCI statement as sort of like a reconciliation statement. It accounts for the difference between the FMV reporting and the amortized cost reporting on the two financial statements. But off the top of my head, there is something inconsistent about this. The two most important financial statements used by large firms and investors are required to be reported on different bases.