I thought they finished the de-stressing project several years ago. I think Conrail/CSX destressed the rails but didn't maintain the records sufficient to satisfy the T. And you don't de-stress rail if it is worn out and will just need to be replaced.
You're right, they did that 2015-2016, we even talked about it here! framingham-worcester-destressing-project-t159622.html
From what's written in that thread, it looks like only track 1 was done west of Framingham.