I see your point Serica, and I agree there has to be some subjectivity involved.
However when interpreting the rule as you describe, the last sentence, "If you feel an issue or topic from an inactive thread deserves renewed discussion, please create a new thread in the appropriate forum or subforum." is redundant and confusing, because it implies that posting in an old thread is not allowed under any circumstances, contradicting the other parts of the rule which you highlighted.
I would therefore suggest removing this sentence.
To give some history for those who weren't members at the time:
The current 'necro post' rule was added in late 2008, together with Rules 2.15, 3.12, 3.13, 4.4, and 5.7, and they were discussed extensively (for some 20 pages) here:
https://www.planetcalypsoforum.com/forums/showthread.php?131253-EntropiaForum-Rules-Discussion
So far as I can see, all the additional rules were created to address specific issues that had been observed as either disrupting the forum, or creating significant additional work for the forum staff at the time.
In particular, there were several threads by members shortly before that time, complaining about not just threads being necro'd but also about multiple new threads being created on active topics.
(Remember the constant 'search is your friend!' posts?
I notice too, that at the time 711 suggested introducing an 'auto-lock feature' on some forum sections, but members seemed to feel that would be too restrictive so the idea was abandoned.)
So rule 3.5 was introduced to give some common sense guidance to members about necroposting - and also, conversely, multiple threads on the same topic, as the same 4mth period is generally applied to merging those.
Personally I don't think that last sentence in Rule 3.5 is redundant.
To be pedantic, the key word is 'from' not 'of'.
(ie: 'an issue or topic from', not 'the issue or topic of')
To break it down:
Why do we have the rule in the first place?
Pointlessly bumping of dormant, inactive threads causes confusion for other members and visitors who may not notice the original thread post date.
What is meant by 'dormant' or 'inactive'?
A thread is considered inactive if there have been no replies in the last four (4) months.
What about if there's a good reason for that particular discussion to be continued?
Posting in an inactive thread is strongly discouraged, unless there is a very good reason for reactivating the thread.
What about if there's something mentioned in the dormant thread that you think should now be discussed further?
If you feel an issue or topic from an inactive thread deserves renewed discussion, please create a new thread in the appropriate forum or subforum.