If the items appear in Outlook (of the destination folder) then Add2Exchange is doing its job well.
If some of the items appear and some don't on the smartphone, you will have to set the settings on the Smartphone to sync farther in the past.
For an IPhone, go to Settings, Mail Contacts and Calendar Settings, then go to the bottom for Calendar settings.
Set the Calendar Sync Setting to All items. The default setting is 1 month, I believe.
This is important because if the item not appearing is a recurring item, or an edited instance of a recurring appointment, the phone must be set to sync the first instance of the recurring appointment.
Also be sure to check this setting in Add2Exchange to make sure you are syncing recurring appointments ever time: http://guides.diditbetter.com/a2e-guide/recurring_appointments.htm?zoom_highlightsub=recurring.
Tip: Be careful not to activate Default Recurring appointment replication on unidirectional private to private relationships because the source users reminders will be rereplicated to the destination every sync cycle without the ability to turn them off.
Hope this helps.