Using DST agents from: https://www-01.ibm.com/support/docview.wss?uid=swg21981718
by default the agent will run on all documents in a calendar year. The agent doesn't just run against the documents that should be modified.
There isn't an easy way to constrain the scope of documents that the agent will modify. We'd like to request to modify these DST agents so it doesn't affect calendar entries outside DST period