Agile PLM Import Behaviour

When we perform import to update attributes on Items with Overwrite import preference, how the import behaves if we are trying to update with same value that is present on Item already.

Does the import overwrites the data even if the value is matching with the same value that needs to be imported? If it overwrites why we are not seeing the updates in history table of Item? Why import is not ignoring the same value update?

Or Does it overwrites value only if there is any difference in the value that in going to be imported compared to the value present on Item currently?