Should old COSC watches come within today's specs?

[crimscrem]

It's my understanding that COSC specs have changed over the past decades. I'm not quite sure what they used to be and how they've changed, but nevertheless, they've apparently changed.

So, let's say you have an older watch from the 70s or from whenever Rolex started getting their watches certified. We know that as part of the Rolex service, they test it to make sure it's within COSC specs. Do they test it for the COSC specs of today (-4 to + 6 seconds)? In other words, to the extent COSC standards were more lax in the past, will the watch now run more accurately after a modern day Rolex servicing?

My initial thought would be that unless mechanical parts or movements are changed that they would not run as well as the modern watches. But then what kind of COSC testing do they do upon service?