Generally the convention is only to link to past threads that have comments - otherwise people click on links, find nothing there, and get ornery. In this case there's only one:

To be great, be good repeatably - https://news.ycombinator.com/item?id=20167310 - June 2019 (46 comments)

I realize your point was a different one about how many times the link gets submitted, but on HN, reposts are allowed unless the thread has had significant attention in the last year or so. A few submissions over a few years, involving one major thread, isn't excessive!

Sometimes I'll post an article and I will be redirected to an older but still somewhat recent thread that doesn't have any comments, so at what point should I be reposting an article to not have this happen?

That happens for the first 8 hours.

The posting on HN may be a few months old but I still get redirected, not a post that was submitted in the past 8 hours. Or am I misunderstanding?

The software will redirect you to a previous submission of the same (more or less) URL in each of these two cases:

(1) the previous submission is 8 hours old or less; or

(2) the previous submission is less than a year (or so) old and got significant attention.

You shouldn't get redirected to a submission that is a few months old and didn't get many upvotes or comments. If the latter is what you're seeing, it might be a bug. Do you remember the link?