Here's my experience for whatever it's worth....

I applied neatsfoot oil generously to top and bottom of my new B17 per Sheldon Brown's directions. I was careful to purchase pure neatsfoot oil, not the oil compund. I found pure neatsfoot at a tack shop. After 200 miles the saddle had taken on a more rounded shape and become comfortable. After 1000 miles to the best of my perception the saddle is unchanged in comfort and appearance from the 200 mile condition. I do not see that it is stretching at all. Basically, the saddle behaved exactly as Sheldon Brown said it would.