Why only some Sovetsky Soyuz names are known

Why do we know only the final planned names for some Sovetsky Soyuz-class battleships?

Those are the names preserved in the archives, and Soviet planners may never have agreed a complete list beyond them.

A complete set of names may never have existed. The surviving Russian archival material supplies only the final planned names now known, and those may be all that Soviet authorities agreed. Naming also operated within a political system in which Stalin's preferences could matter. The absence of further names is an evidentiary limit rather than proof that historians have lost a finished list.