Hi David--
I'll bite!
I'm an Aperture user and haven't yet migrated my large referenced library to another tool yet...but I'm always testing other tools and have grown to like C19 because the image quality is pretty awesome. For me, I think C1 needs another turn or two of the crank in the image management department before I decide to leave Aperture
Anyways, I use ExifTool as part of my workflow: I have written a few command line scripts to write metadata into the RAW file...which seems similar to what you want to do.
You say Aperture has been managing them fine for years; specifically, how are your images sorted in the Aperture? Are you using a Date sorting scheme, or name, or some other?
Since many of your images may not have Capture Dates in the Exif data, Aperture is probably using the Created On date of the file. Sometimes, this data is available to ExifTool--and if it is, it can be written into other areas of the file.
If you post a file and note what date it should have I might be able to scribble out a command that you can use to process your files.
thx
PP