The only reason why I think that there are people saying that vintage Coticule stones are
better for straight razor use then new Coticule stones is the following:
Most of the vintage Coticule stones that you guys find on eBay or in your local antique store are stones used by barbers or by private straight razor users. The Coticule miner companies from 100 years ago selected these stones specially for the use of straight razors. Before World War 2 there was a large exportation of Coticule stones for straight razor use to the USA and UK. So most of the vintage Coticule stones you guys are finding in the USA and UK are perfect stones for straight razors!
After World Ward 2 there only was a small exportation to the USA and this came to an end around 1960-1980. Around 1960 the last mine closed and in the '80's the last quarry went broke. So a lot of the Coticule knowledge disappeared (knowledge in terms of 'which Coticule is good for which use').
We, Ardennes Coticule, officially restarted the last quarry in 1998 and are planning to re-open the last mine in 2009. In our family (Ardennes Coticule is a family business) we have a lot of knowledge about quarrying and mining (The Coticule quarry and mine aren't our first quarry and mine) but we didn't had much knowledge about the Coticule stone (both in terms of the use and the distribution world wide).
So in the very beginning we sold every Coticule for every purpose. None of our family members knew that for example straight razor users preferred softer stones and wood workers the harder ones!
We had to learn all this from unsatisfied customers, from talks with Coticule users from the old days and so on ... .
The Coticule stones sold by us in the beginning of our company are Coticule stones from an excellent quality but were sold for the wrong purpose (example: not soft enough for straight razor use)!
But that's the past. Right now costumers have to specify the purpose of their stone and they will receive the right Coticule stone!
All the stones sold by our USA and UK distributors for straight razor use are excellent for that very purpose and are even good as the vintage Coticule stones!
But keep in mind that we are working with natural stones! All the stones are unique and sometimes we have Coticule stones that are extremely soft and that contain a very high concentration of garnets.
If you got a vintage Coticule like this you could easily say that it's better than a 'new' Coticule but you can also find a vintage Coticule which is harder and/or contains less garnets then a 'newer' one.
So I'm sure you guys understand that there are Coticule stones floating around in the straight razor community that are less suitable for this use. Are these stones bad? No, they are excellent Coticule stones, but not suitable for straight razor use.
It all depends on the vein from which the Coticule comes!
More info:
Coticule Layer Round Up - Part 1 (Warning - 62 pictures) - Badger & Blade