The so-called "Synchronization Window", namely the portion of remote calendar synchronized with the device, is a setting that can be found on all Android devices under
Settings -> Accounts and Sync -> [Your Account] -> Settings -> [Your Account] -> Period to sync calendar.
Each brand/version has its own settings, ranging from 1 day to All.
The Synchronization Window can also be seen in the ZxMobile logs:
2012-04-14 18:33:50,385 [ZxMobile Handler Thread] info Ping: Getting items older(or newer) than 31 days for type: 5 on folder: /Inbox 2012-04-14 18:33:50,392 [ZxMobile Handler Thread] info Ping: Getting items older(or newer) than 14 days for type: 11 on folder: /Calendar
If you think some items are missing please verify that such items are not out of the Synchronization Window.
Example: Setting the Synchronization Window to 2 weeks will only synchronize the events of the last FOURTEEN days and all future events.