Index consideration for date effective tables

it is a best practice to add ValidTo to the ValidTimeStateKey index
and on the Properties tab (of the ValidTo field in the index) to
select Yes from the Included Column.

[see: http://dev.goshoom.net/en/2012/04/included-columns-in-ax2012]

but if it is a clustered index see this:

Performance considerations when designing valid time state tables
To help improve performance of valid time state tables, you should index them correctly.
Valid time state tables are modeled with an alternate key that includes the ValidFrom column.
In some models, the ValidTo column may have also be included in the alternate key,
but this is not necessary for uniqueness, and it should be removed from the alternate key constraint.
If the ValidFrom column is a key column of the clustered index,
the ValidTo column should not also be a key column of the clustered index.
If the ValidFrom column is a key column of a non-clustered index,
the ValidTo column should be made an included column in the non-clustered index,
which provides coverage for range queries that involve both ValidTo and ValidFrom columns.

for examples see where the index is a clustered index see:
\Data Dictionary\Tables\LogisticsPostalAddress

or see
\Data Dictionary\Tables\HcmPositionWorkerAssignment