Date/Time, EXIF and Lightroom

Question

I am quite aware of the past thread on the date/time issue started by Judy
Nicholls. But id did not help me to solve a mystery I am experiencing with a
bunch of jpegs made shot some years back.
Lightroom states that these files have no date - none is shown in the metadata
panel to the right, and they are selected in the metadata browser when selecting
"unknown date".
But several EXIF reader programs, including EXIFUtil, EXIFEditor and EXIF Pilot
clearly show me that the three relevant EXIF dates are there, are correct and
are identical. The EXIF header, the whole metadata section, seems to be complete
and readable outside LR. Oddly, EXIFER shows a date of "3--DEC-99" for Date
Taken in its file listing, but then shows the three relevant date entries
correctly and identically when doing an EXIF edit.
Why can't LR read these dates?
As a test, I tried to add the capture date through the menu (Metadata - Edit
Capture time ...), and it LR reacted to the added date by putting the file among
those with a known date (2003). But it did not change the EXIF data in the file,
apparently only a date in the LR database. I exported XMP to the file, read the
resulting data with EXIFUtil - but could not find any difference with the
original file!
Can anybody explain what is going on here?
Chris

Answer 1

Ok, here's what I've found:
If the "xmp" sidecar exists and you do "Read metadata from file", it will read the metadata from the "xmp" sidecar. If the "xmp" sidecar doesn't exist, then if you "Read metadata from file" it reads it from the image itself.
Thus, if you have an "xmp" sidecar file that exists and use an EXIF editor on the original image, the EXIF time change will *never* be imported again from the image file no matter how hard you try (ie: it will be ignored). If you remove the "xmp" sidecar, then you can get it to read the EXIF time data from the image. I don't think you have to "reimport" as some have done, but rather just delete the "xmp" sidecar.
However, and this is important, if you've already made Develop edits, those edits will be lost on the "Read metadata from file", import of EXIF data from the image.
If you think you'll be tricky and move out the "xmp" sidecar, edit the EXIF time data in the original image, import the metadata from the image, move back the "xmp" sidecar, and re-import the metadata and you'll get the best of both worlds, well no, you're SOL. The "xmp" sidecar date/time overrides the EXIF date/time previously imported.
So, I'll probably be stuck exporting my RAWs, then fixing the EXIF time data after the fact in the JPEGs since I've already made tons of edits across my 1,000+ photos for this batch.
Incidentally, iMatch by Photools can do a batched EXIF time correction by partial or full hour offset (or day) and Lightroom seems to be happy with the EXIF date format. iMatch is a pretty nice tool in of itself and probably better for general photo organization at least in the iteration of Lightroom (it is not a RAW converter though).
It can also do edits of XMP data, including with Visual Basic like scripted edits, so perhaps I can eak it out to do the fix that way (or re-export the fixed EXIF data into the XMP data without touching the rest of the Develop edit data also there).
Yuck!
Lightroom is a very nice app, but it's certainly still pretty "beta" in many respects.