The identity-related data are copied to each event, yes.
This concerns affiliation, writing of the name, academic titles, everything. (I am not sure about the email address.)
That means, whenever it is edited in the event afterwards, this edit will remain persistent. If the origin (user profile) is modified, it will not propagate to all events/contributions.
However, you seem to report, @jouvin, that the data are not taken from the profile, if the same person is removed from and event and added again. Or did you really mean contributions (which I guess are taken from the data in the event registration/participant)?
@ThiefMaster, maybe you can clarify: Are the personal data copied from profile to event level and from there to contributions, or do data in contributions of the same event remain linked (identical) to each other? How does it work exactly? Maybe such a paragraph could go into the documentation.