No respones for ModifyDate for tif file

[siamak]

I use exiftool -s -s -s -exif:ModifyDate file in my programs. It works on NEF as well as JPG and reports the date. But, in tif files only blank. I can see all dates when ask to show all values of the tags. checking it with -G1 switch it shows that Modification Date is in System rather ID block. I tried without -s and no luck. Do I missing something?
These tif images are scanned.

[siamak]

I found the solution! I guess with tif files I need to add Change ModifyDate to FileModifyDate. Strange in NEF and jpg it does not need it!

[Phil Harvey]

The FileModifyDate is a filesystem property, and isn't stored in the file itself.  An EXIF compliant TIFF image should contain EXIF:ModifyDate, but a non-EXIF TIFF may not.

- Phil