Should I edit a closed issue with the issue summary template? Once you go to create a new issue in drupal.org you can see a message that says:


  Learn how to report an issue. Use the issue summary template to
  summarize the issue in the Description field below. Others can also
  change the summary. Editing the summary does not subscribe you to the
  issue or notify subscribers, so add a comment describing your changes
  after any significant edit.


But there are some closed issues like Incorrect call to urldecode() in the www.drupal.org site that don't follow the template format.

Should I edit a closed issue with the issue summary template?
Yes. It's completely appropriate to edit an issue to clarify the findings, solutions, workarounds etc. and make it easier for people who may look to that issue for reference.