So I recently got the mod that fixes these broken templates for Future Sims. But I was curious was this broken template also something you could accidentally put on a Sim in CAS, Like is one of the preset faces or head options in the tabs, or is it like some hidden template generally only applied to Game Generated Sims (vs CAS sims.) And if so, where in CAS are they?

It's two of the templates that are available in CAS. But what mod did you get? Since that will probably fix the templates in CAS too.

It was the one Sims Wikia linked to. Looks like it was done by someone called Argon and it was up on "More Awesome Than you"

Yes. Placing argon_archfix will fix those templates in CAS for future sims.

Sims who are already built with it - Gothboy Tricou, the Ruben Bros., anybody you built with those two templates, etc. - will still have broken faces, and will pass them on to their children.

The broken face just means that sims with that template revert to a different (default) template in old age. It isn't an extra hidden face.