This is how I the data sync works between SSP and Site Collection. The data is imported to SharePoint SSP from active directory and from SharePoint SSP to SharePoint Site. So SharePoint SSP sits in between SharePoint site and Active Directory. The data from SSP flows based on the configured sync (full or incremental).
When someone adds a User into a Site Collection through a People Picker the profile will be created in the SharePoint site with the most current information available on SharePoint SSP at that point of time. Profiles on SharePoint siets are not updated automatically/incrementally from the SharePoint SSP. So if there are any changes made in the Active Directory they will not be reflecting into the SharePoint Site. Hence the data between Active Directory and SharePoint Site is not in sync.
As a workaround to fix this issue we can delete the profile from Site collection and re-add this into the site collection. This will force the site collection to pull new data from the SSP. It may happen that this process will not work for first time. Trying to do this process multiple time should get a profile with most recent data from the SSP into site collection.
You can also find interesting to read User Details are not showing in the SharePoint Site
