[Brightcolours]

I think the lens is "reasonably" well centered so Sony Australia may just take that as a reference.

 

Honestly, astigmatism alone doesn't explain those borders.

Well, a few test images will tell a lot. 

Consider this lens:



In your and other MTF based reviews it does pretty badly in the corners, so much so that the lens has a bad reputation. But in real life usage, its results are pretty good (obviously not the best lens in the world at this focal length).

Shooting at MFD reveals very strong astigmatism, which explains the poor border/corner results in MTF tests.

 

Here an example past MFD (with 12mm ext. tube) to show the problem very clearly:



 

And here the same lens at a more normal (for the lens type) focus distance:

Quite nice performance of this little pancake lens.

 

I am not saying that astigmatism IS the big bad bug in the MTF results for this Sont 16-70mm f4, I am just suggesting that it just might be an explanation for the difference in the MTF results and the images. Yes, the images never are tack sharp in the borders, but they are also not as bad as the MTF results suggest. A few real life images at MFD should show if astigmatism muddles the results.