Sorry to post these late, I had some trouble with uploading pictures for a little while!  Here are some black mission breba pics from earlier this season.  The tree was cut back pretty hard this year to teach it a bush rather than tree shape in pot and has recovered very well, the brebas were fewer in number given the pruning, but very tasty!  If anyone is interested I have a few trees left and would be more than happy to trade for new varieties.            

It looks good.
I question the variety based off of the one leaf you show and the lack of any amber with the red flesh however. If that leaf is the typical pattern, I would think more along the lines of Vista Black Mission or just Vista which is not the same as Black Mission at all. If you bought the plants at a store though, I doubt they would be Vista.

I cant get to the mother tree right this second, but I assume that leaf was anomalous. These pics are from rooted cuttings from the mother tree and are all consistent with each other.          

I'm not experienced in judging leaf shapes.  Are these leaves more like what they should be?  The tree was given from a friend to the family years back.  Not sure of their source.