In most cases you should net revive old threads exactly for that reason that the old discussion might be obsolete.
Thread Necromancy is in general frowned upon and thus against the rules. There are exemptions (especially in the "Fun Forums") but in most cases creating a new thread is the right course of action.
You can always create a new thread and link the old thread in your OP.
This is, in general, also valid for bug reports. Bug reports are most often tied to a specific game version which is included in the OP. So if a bug persists over several versions it's in most cases better juts to create a new bug report thread.
Besides of that there's always the "Jump to new" button which leads you to first post you haven't read yet. The forum software considers all posts beyond a specific age (I don't know how long exactly) as "read". So if someone revives a thread sufficiently old that revival post would be considered as the first
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and you can create threadmarks for easier navigation
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