I've got a database with the following structure:

    Elements table
    +------------+---------------+---------------+-----+
    | element_id |    user_id    | element_data2 | ... |
    +------------+---------------+---------------+-----+

    Tag categories table
    +-------------+---------------+
    | category_id | category_text |
    +-------------+---------------+
    
    Tag values table
    +----------+------------+
    | value_id | value_text |
    +----------+------------+
    
    Tag-element relationship table
    +----+------------+-----------------+--------------+
    | id | element_id | tag_category_id | tag_value_id |
    +----+------------+-----------------+--------------+

An element can have multiple tags associated with it, even multiple values on the same category.

What the app does is to let the user put new `tag_values` as unique elements (categories right now are not user-editable, but may be in a future). As they are not associated to the user, if two users write the same `value_text`, then the same ID is assigned to it.

So, to have a data sample, the `tag-element` table - the most important here - would look something like:

    +----+------------+-----------------+--------------+
    | id | element_id | tag_category_id | tag_value_id |
    +----+------------+-----------------+--------------+
    |  1 |          1 |               3 |            9 |
    |  2 |          1 |               3 |            5 |
    |  3 |          1 |               6 |           13 |
    |  4 |          2 |               6 |            2 |
    |  5 |          2 |               5 |           15 |
    +----+------------+-----------------+--------------+

The question
----------
As such, there is a category called `game_date`, which stands for the date where the element (that is an event) is celebrated. 

Should the `game_date` values be stored as the other values, so two equal values for a date have a unique ID, or its uniqueness makes its performance poor? 

I mean, it can be possible for multiple events to be on the same date and hour, but I don't know if it would be better another kind of structure where that date is stored as a `Date` field on any of the tables above. *Just as the `game_date` can be also other categories involving date (such as `game_recorded`, etc.).*

Thank you!