Okay, I realize this all sounds pretty darn crazy, but I've got more info on this.
First of all, I think the only reason that 2003 and 2004 were behaving this way, while other filled dates were not, was that they were recently updated and had yet to be written to tag from the library.
I say this because I discovered that ALL unfilled "Date" tags are showing in file type info as "1899/12/30". Moreover, these empty date fields are ordering themselves in the date column as if that were their filled value. They sit between the earlier dates I've filled for classical music and the later dates for pop. NOT on one side or another, as you would expect for null entries to order themselves.
I tried putting a date in an empty field and writing it to tag. The correct date was reported to the tag. I then overwrote that date with null (by backspacing over the entry in AW/tag info), and the date of "1899/12/30" returned.
I don't know how long this has been an issue, as I usually turn off "update tags when file info changes", and only maually update tags every now and then. This might have been going on for a year, for all I know. I only recently started examing the tag info directly through "file type info" and this little beauty appeared.
Hope somebody has some insight to this, or at least I hope somebody can reproduce this.