Thanks for your posting. TestRail currently does not store the status of the defects/issues and we recommend using the test statuses to indicate if a defect/issue was fixed. For example, if you find a defect for a test, you would usually add it to the Defects field (and to JIRA or Redmine via TestRail’s integration features, etc.) and then mark the test as failed. Once the defect has been fixed, we recommend setting the test to Retest and eventually to Passed once the fix was verified again. This is then reflected in the Defects > Summary reports which also include test results etc (so, a test with the Passed status would indicate a fixed defect, a Failed status an open defect, etc.).
I hope this helps and please let me know in case you have any further questions!