The millerandage Pinot is from a massal selection of Pinot Noir known as the Valdivieso selection. It is not from a climatic incident as is usual on the grapes.

When I first started to make wines in Chile, back in 2002, I was attracted from the beginning by Biobio as a cold climate region that would suit really well varietals like pinot noir and chardonnay (which have to mature slowly to express the whole of their complexity).
VC Family Estate already had some vineyards planted with pinot noir and chardonnay there, near the small village of Negrete, in an area called Santa Ana.
The soils in Santa Ana are alluvionnal. They can produce very good fruity wines bit you would never get great terroir expression from them because they are not complex enough in terms of minerality. 
So, we decided to plant the hillsides from Millaflores nearby, very complex volcanic soils with a lot of diversity in terms of their mineral complexion. A type of soil with its own unique geology easily transmitable in a grape like pinot noir. 
Meanwhile these vineyards were going to produce, I was still looking at the Santa Ana plantations to learn how the different "Dijon clones" 115 and 777 , we performing in comparaison to the Chilean National selections. 
At the same time we started the Veranda label with chardonnay and pinot noir fruits we were buying from Casablanca (in region of Valparaiso).
The farm where these fruits were coming from also had the "Dijon clones" 115 and 777 plus two of the Chilean National selections.
These Chilean National selections are old massal selections who had been introduced to Chile about 60 years ago or so, back then in order to make sparkling wines.
Two of these selections are named after the producer who had introduced them, one is known as the Concha y Toro selection and the other one as Valdivieso selection.
At the beginning I was kind of snobbing them, thinking the newer Burgundian clones would be superior.
On the top of that, among the growers, they did not have a great reputation because they were not cropping consistently. This was especially true for the Valdivieso which had really bad reputation among the growers because of it consistent tendency to produce "millerand" fruit every year, no matter what the climate is that year. The phenomenon is probably due to some genetic factors that ends up in a bad flowering and result in that poor fruit set.
You can look at that with a different view, considering this is a way to obtaini berries of exceptional maturation.
In 2003, when I visited the vineyard we were buying the fruit from in Casablanca, I noticed these beautiful millerand (also known in englis as head&chicken) in the Valdivieso selection block.
The growers wanted to pull out these rows.
When I tasted these berries I immediately noticed an amazing concentration, great potential structure with softness in the tannins.
I gave the instructions to my team to vinify all these Millerand grapes apart. I was in the aim to produce a great wine and wanted to convince the grower not to pull them out.
We made 3 casks of that wine that year, the first Cuvee Millerandage. The wine was concentrate, balance with power and finesse. A Russian tasted it and bought it out.
The following year the grower pulled out these vines to plant more productive clones. What a sadness.
I thought then, the Pinot Noir Cuvee Millerandage would be a one year only attempt that would benefit to the pleasure of one Russian guys and all of us what had the joy to create it.
A few years later, after we had bought these vineyards in Quinel (in Biobio), inspecting them with the vineyard manager there, we noticed there was a block, on a beautifull complex soil, that was randomly planted with some of the Valdivieso selection all over it.
After I had been dancing in joy, I gave the instructions to harvest these vines apart. This is how the new Cuvee Millerandage 2007 was born. We made 10 casks we have not told our Russian friend yet, so more people can enjoy it.
We have now a small program where we reproduced more of these vines to have a block with solely Valdivieso selection to have more of it and to make it easier to grow and harvest.
The good news is the new Cuvee Millerandage grows on a much better terroir and under a more appropriate climate in Biobio.
Do not tell the Russian.