The heading Kievan rus' was instituted in 1992 and has been used inconsistently by LC. According to the array of subject headings, it seems that Kievan rus' shouldbe considered as an earlier form of Russia/Soviet Union.

What follows are the authority references for Kievan rus'.

KIEVAN RUS'
--History--To 862
--History--862-1237
--History--Vladimir, 972-1015
--History--Mongol Invasion, 1237-1241

but there is a major inconsistency:

Kievan rus'--History--Vladimir, 972-1015
UF Soviet Union--History--Vladimir, 972-1015
Use for reference, signifying that Kievan rus' and Russia/Soviet Union are the same entity.

but

Kievan rus'--History--862-1237
BT Ukraine--History--862-1240 Broader term reference, signifying that Ukraine is a broader term than Russia/Soviet Union.

There are also the headings:

Russia--History--To 1533
and
Ukraine--History--To 862
Ukraine--History--862-1240
Ukraine--History--To 1648

Based on an analysis of LC practice, it seems that Kievan rus' is used only when mentioned explicitly in the title (Kievskaia rus'). The term Drevniaia rus' appears to get the subject Russia.

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Examples:

Original record: DCLC82186973-B
Rybakov, Boris Aleksandrovich, 1908-
Kievskaia Rus i russkie kniazhestva XII-XIII vv.
...
Russia--History--862-1237.
Ukraine--History--To 1648.
Slavs, Eastern--History.

Revised record:
Rybakov, Boris Aleksandrovich, 1908-
Kievskaia Rus i russkie kniazhestva XII-XIII vv.
...
Kievan Rus--History.
Slavs, Eastern--History.

Original record: DCLC94174208-B
Gobarev, V. M. (Viktor Mikhailovich)
Predystoriia Rusi. (A history of the area before Kievan Rus')
...
Kievan Rus--History--To 862.
Add:
Russia--History--To 1533.