I notice the difference between the bottom and the top. That would not work for me either! Problem is, SAs will argue the "distressed" character of "crumpled calfskin"; they will state how each one is unique.
Definitely try to exchange for a more consistent distressed leather. I fear it may be an uphill battle, however, unless you work with a really conscientious SA. Very few of these bags were released, most were pre-ordered and reserved.
Having pre-ordered my so-black handbags this season, my SAs sent me pictures of multiple bags and I was able to choose. Some that were in that selection of both the so-black Boy (bowing) and so-black jumbo (wrinkling) were NOT up-to-par. Sadly, what's leftover of these limited handbags may be the ones declined by pre-order customers. I agree that this should NEVER be the case. Chanel quality and standards SHOULD absolutely be consistent. The unfortunate truth is they simply are not.
I would definitely keep searching. Contact the Chanel hotline if you are in the US. However, I would not keep this particular bag unless you are willing to accept the inconsistency due to the fact that it is a rare and unique mini - and cannot locate a suitable replacement.