Hi
Thanks for your reply.
The stitches are not white but cream (poor light here in London these days). I have been told that this is the very much sought after 5002 brown buffalo strap IWA05943 (the 155 version). I think IWC changed the straps for the 5002 in 2005/6, and it appears that this one cannot be ordered from AD anymore. In fact, I rang Wempe in London and they told me that they do not have any in stock and that they can only re-order the standard brown one.
Anyway, I bought it (it is brand new). I have a black croco on my BP that I love, so I am not sure I am going to keep this one.