For C-ISAM, we encountered the same problem for a numeric field which we had set it as no negative sign in the file definition and the value of the field is a negative value.
For your case 1:
Did you check the Last Day Updated in Control File? Would it be possible that
dates in certain files are updated using system date (@DATE) and some of them in
other files are updated using Last Day Updated.
If some one has run the End of day until the 07/26/2003, then your Last Day
Updated will be stamped as 07/25/2003.