Hi outsmart,
At the moment, I can only suggest that the dates by Oppolzer and from NASA are not in agreement. I assume you have downloaded their Catalog:
http://eclipse.gsfc.nasa.gov/5MCLE/5MKLE-214173.pdf
where the Introduction provides a narrative on the development of the Canon from Oppolzer's time
When you go to http://eclipse.gsfc.nasa.gov/LEcat5/LE-0599--0500.html scroll down and select for example, 03460. That then shows the path of the eclipse for -567 July 04 (that is 568 BCE of course), and explains the reason it was predicted but not seen.
Did you have a go at the Javascript tool at:
http://eclipse.gsfc.nasa.gov/JLEX/JLEX-AS.html
If so, tell me what your input criteria were (select Baghdad for simplicity sake) and tell me the results you got for say 568 BCE (-567). How do these compare with Oppolzer?
I shall make enquiries. Maybe others can provide some illumination on this?
Always remember that the issue of the dates is only a concern for the WTS. The responsibility for verifying dates is their problem, but every time they remove faith in the accuracy of a secular record, they remove a plank from their foundation.
Doug