IBM Quality Manager provides an API for accessing the history of individual resources as well as the history of archived/deleted resources. You can read about the supported resources types and more on https://jazz.net/wiki/bin/view/Main/RqmApi#historyUrl
The URL for the history of a given resource looks like <integrationUrl>/history?resourceId=resources/<projectAlias>/<resourceType>/<id>
Test Plan URL
History URL for the Test Plan
The history is provided as a data feed where each entry has a title, the time of the change and an XHTML description of the change.
NOTE: the QM REST API does not provide a schema for the history feed so I have put one together here https://ibm.box.com/s/aco4thbmnspqzmg0nse2mdzcgc1z8vqy The schema is provided as-is and you can freely modify it to suit your needs.
A template example using this schema is available here https://ibm.box.com/s/anr5tgqro6pmodng137zapqmdp7c4tlj
NOTE: the tables in the XHTML description of the change can contain long texts ( URLs). To avoid the Word/PDF document from overflowing the page margins please check this article https://rpeactual.com/2015/08/03/allow-tables-to-extend-into-margins/