Thanks. I guess the 1 paragraph in Marko's message tells me that MC can't edit EXIF dates, if I read it correctly.
Unfortunately, I want to organize all my scans/photos now, not "later", so I'm going to reverse directions and simply use the Lightroom dB for all my scan/photo querying and slideshows... I was using it for editing anyway. The metadata handling there is actually much more powerful than I realized and the more I use it, the more comfortable I feel with it. As Marko states, and as I've come to realize, the Image portion of MC is just not high on the totem pole of development focus right now.
Cost me 7-10 days of lost effort
but it could have been a lot worse.