When copying SharePoint objects that aren't content in a list or library (Lists, Libraries, Content Types, Workflows and others), the Creation Date (or Created Date) will be changed to the date of the migration and will not preserve the source's Creation Date.
The SharePoint API doesn't allow setting a custom Creation Date when creating or modifying these items. Unfortunately, there is no way around this limitation.
An example of this is the Archives web part in Blog sites. It refers to the Posts list's Creation Date to determine which months to show Archives for in the side bar. When migrating a Blog Site, the Archives web part gets reset to the current month. It will show no data for older articles, even though they display the source's Creation Date, as the Posts list itself now dates from the migration.