Question

How does the order of data load affect the OV?

Answer

In theory, it doesn't matter because the admin can choose OV rules that ignore chronology (E.g. Aggregation, Frequency..) but if the admin chooses Recency as the OV rule then the LUD (last update date) is used to determine which crosswalk value to use. 

Attributes that were recently updated (with the maximum number of update dates) will have the highest priority to be marked as OV. LUD is the default survivorship strategy.

The winner value is calculated in this order:

• For each crosswalk bound to the value, the maximum number of update dates is obtained from: singleAttributeUpdateDate, updateDate, and sourcePublishDate. The list of update dates for each crosswalk is produced.
• Finds the crosswalk with the most recent update date. All values that were provided by this crosswalk became winners.

• If the value has the most recent singleAttributeUpdateDate, its crosswalk becomes a winner crosswalk. If there are many values provided by this winner crosswalk, all of the values become winners.
• If there are many crosswalks with the same update date, only the first crosswalk becomes a winner.

References

https://docs.reltio.com/matchmerge/survivorshiprules.html