Because the leather is a natural product (well, as natural as taking a dead cow's skin and soaking it in unknown nasty chemicals can be!), you get hard ones and soft ones. Some are pretty soft from the off and never noticeably break in, some stay hard but visibly break in after 1,000 miles or so (fine creases around the sit bone contact area). Some never break in at all; I commuted on a Spa Wharfe for a couple of years and it remained unaffected, and as hard as concrete. Never rode it more than 10 miles at a time, and wouldn't have wanted to. It broke a nose bolt bracket (Spa sent me a new one for free) and then popped a rivet (not easily home repairable) so the hardware was weaker than the leather!
There is an oft-repeated theory that honey Brooks are softer and more easily broken in, if they even need it, than the black ones. My experience of about 7 different Brooks saddles tends to bear this out. My honey Swallow and Team Pro were soft from the off and have stayed smooth, with no visible break-in. My black Swallow is harder and quite clearly broken-in at the back. My favourites are the large rivet vintage dark brown Professionals (not Team Professionals, which are a bit longer) which were "pre-softened" from new and just work.
