I have several Plan Project in my Jira and I can't see any completed issue within the Plan view where all issuetype hierarchy is shown. Even though I set in the Plan configuration the number of days after the completion to 200 as you can see in the picture below:
Essentially in Jira the resolution field should not be NULL (it shows up as "Unresolved" - internal representation of NULL for the field) for completed issues. You may also need ensure your plan's issues sources are setup properly.
If you set your issue sources against a board (i.e. SCRUM or KANBAN), then your completed issues WF statuses need to be located at the last right column (terminal column). Otherwise, those issues will never be truly "COMPLETED" in the Jira system. Example, if you try to close out a sprint where those issues are not in the status associated in the last right column, then Jira will ask you to move those issues to another future sprint or the backlog.
Hope this helps.
Best, Joseph Chung Yin
Jira/JSD Functional Lead, Global Infrastructure Applications Team