While I am certainly open-minded about the possible existence of anomalies, the facts remain that:
a) "All known cataloged versions of black-dialed Ingenieurs have a black date window -- that is, white date numbers on a black background." source: the oft-referenced Dial Variations article
b) the vast majority of both Ingenieurs and Yacht Clubs with black, grey or blue dials feature dark date disks, further suggesting that IWC was typically consistent in the use of darker shades with darker dials
c) the vast majority of those 666s that now feature white disks are not owned by the original owner, and so there is a possibility, if not probability, that the disks or dials were changed at some point over the past 50-60 years
These points lead me to the conclusion that if there were anomalous black/white examples that left together, they are very rare, and that therefore, barring a compelling provenance, all such examples should be treated with skepticism. This is especially true of examples such as the subject watch, where there are other questions relating to originality.
Regards,
Tony C.