I have a couple hundred newsletter subscribers, but I've only written 1 article that I keep updating... Should I rather make a new article with each version, so that subscribers get an email notification?

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If there are going to be 100 versions, then don't publish a new one per update, as it will hurt the subs in the long run.

You can use semantic versioning & publish brand new articles for every major article.

Or 

You can publish TLDR;s linking to previous ones.

Imho, publishing new articles is better (but sign with version).
Versioning your articles can be a great approach.

I would right a complete new random article completely off top pic!! The one article and its versions are great which demonstrates the ability for a second that!

I think it's fine the way it is.
I think it's fine that the registrant is waiting for a new article that may be there someday.