The first batch released (primarily in the Asian market) had a battle damaged chest piece that did not fit correctly onto the figure. It was because HT placed the pegs that hold the BD chest piece a little too low.
You could clearly see a gap throughout the bottom edge of the BD chest piece when placed onto the figure.
Hot Toys put a stop on any further shipment to fix the problem.
As a result, the Mk.VI figure was delayed about 2 months from its original release date.
With this 'fixed' batch just recently released, HT was able to "adjust" the pegs on the BD chest piece and it now fits snug and flush onto the figure's chest. No gaps.
However, it's also possible that HT also enlarged the holes on the figure where the pegs insert into. So now, there have been a few reports that the non-BD chest piece fits somewhat loosely.
As more Mk.VIs make there way into customers hands, I'm sure we'll learn more.