Just a thought. In a couple of those pictures you can see where the hole for the 4th 50 exists but has been patched over and the patching looks pretty flush with the wing and symmetrical. Perhaps on the p47s that were made with 6×50s( assuming those articles I read were acurate) instead of changing the manufacturing process they made them like any other p47 then just patched the hole where the 4th 50 went. If one were to desire to make a few hundred p47s in such a configuration that would seem to be the best way to do it rather than make a change to the wing manufacturing process for a few hundred planes.
So maybe one or two of those pictures are factory 6 gun Thunderbolts...........or maybe not.