Should I add custom dubbing to my older videos too, especially the ones still getting traffic?

I’ve started using custom dubbing on my newer videos and have noticed some additional traffic from it, which is encouraging.

Now I’m wondering whether it’s worth going back and adding custom dubbing to my older videos as well, especially the ones that are still consistently getting views.

Has anyone here tried this? Did dubbing older back-catalog videos lead to meaningful extra reach, or is it usually better to focus only on new uploads going forward?