I guess the larger question is that the typical routine? - a cursory look shows for 2022 the mix for Lafite is 94% CS, 5% Merlot, 1% PV and for Carruades 53% cabernet sauvignon, 40% merlot, 4% cabernet franc and 3% petit verdot. Maybe my epiphany is that it has always been that way for Lafite with their second wine being more Merlot based. I suppose I never considered that these estates have second wines that are so dissimilar in blending mix - I always thought it was more just deselected fruit across a broad spectrum. I guess the question is why doesn’t Lafite just plant more CS to put into their first wine since the ROI seems like it would make sense.
Some other data points:
2018 Cos: 74% Cabernet Sauvignon, 23% Merlot, 2% Cabernet Franc, 1% Petit Verdot
Pagodes: 54% Cabernet Sauvignon, 37% Merlot, 6% Petit Verdot and 3% Cabernet Franc
2014 Margaux - 36% of the year’s total production and is a blend of 90% Cabernet Sauvignon, 5% Merlot, 3% Cabernet Franc and 2% Petit Verdot.
2014 Pavillon Rouge - 22% Merlot, 77% Cabernet Sauvignon, 1% Petit Verdot
2008 Margaux - again 36% of production 87% Cabernet Sauvignon, 10% Merlot, and the rest Petit Verdot
Pavillon has 26% Merlot in the blend.
2016 Lafite - 92% Cabernet Sauvignon, 8% Merlot
2016 Carruades - 44% Cabernet Sauvignon, 49% Merlot, 5% Cabernet Franc, 2% Petit Verdot
At least for Lafite as I dig into this question a bit more they actually have some plots of Merlot designated for the Carruades so it is typically much more Merlot based.
2022 Palmer 51% Cabernet Sauvignon, 45% Merlot, and 4% Petit Verdot
2022 Alter Ego (which they don’t say is necessarily a “second wine”)
51% Merlot, 43% Cabernet Sauvignon, and 6% Petit Verdot.
So Palmer is more what I might expect with the blend not too different - Lafite obviously consistently makes their second wine with more Merlot and Margaux appears to vary based on what nature gives them although also often putting more merlot in the Pavillon (for the '22 vintage it is 24% vs 6% in the Grand Vin). Sure these are broad generalizations but it reminds me that the second wines aren’t necessarily just slightly inferior versions of their siblings but actually can be very different in composition. And if you like Merlot then maybe you should look for the second wines!