The term "Deployment" in the vernacular of WSUS refers to *APPROVALS*.... so the LastDeploymentChangeTime will change anytime the Approval state of an update is changed.
This would occur when a revision is posted because the approvals are shifted from the older revision to the newer revision.
Your better bet for identifying the original first creation date of a specific KB is to use the actual creation date.
From the public views this would be found in the field CreationDate in PUBLIC_VIEWS.vUpdate
From the API that would be IUpdate::CreationDate.
You could also use IUpdate::ArrivalDate if you're more interested in when the update was inserted in your WSUS database rather than when it was authored.
I see. Then I have already making a mistake of using LastDeploymentChangeTime !
If I have only ( and can only use) wuaapi (v2.0.50727), of which does not seems to have any property close enough to CreationDate in any of the interface, what can I do?
I hope I search and look through enough the wuaapi MSDN help and IUpdate...IUpdate5...
These fields come from the *WSUS* API, not the WUA API.
You cannot get update metadata from the WUA API, the only thing you can do with the WUA API is direct it to scan/download/install updates.