The modern layout is as you will find it today and in roughly the last ten years.
The classic layout is inspired by a few videos I found on youtube. The most important are two onboards from 2006, when the stage was run without the roundabouts. The tarmac between the roundabouts and Duesaigües is very broken, and there are huge muddy cuts in every corner. There are no guardrails in sight. As you'll notice, the section along the reservoir was brand new in 2006 with perfectly smooth asphalt.
https://www.youtube.com/watch?v=AjtSONYFQjM&list=LL&index=64
https://www.youtube.com/watch?v=UCA-xvcJ55w&t=276s
Additionally, the very first passage in this excellent video shows the section along the reservoir in 2002, with fantastic action from Petter Solberg! Here you can see that the road surface along this section was a bit older, and missing the concrete 'kerbs' that are a defining feature of the modern layout.
https://www.youtube.com/watch?v=XSLxAws_10c
The classic layouts combine both. The roundabouts and the Teixeta section along the highway were only featured in 2007 and later, but I included it in the classic layouts anyway.