Template:Undelete year category
Note: If you are basing the date on "70 years after the death of the author", note that according to the legal definition copyright expires on 31st December of the calendar year of death. So, the file becomes copyright free on 1st January of the following year. The correct year category to use is thus Year of Death + 70 + 1 unless the country of origin has a copyright term of less, or more, than 70 years.
Important: You must include the deletion request subpage in the category, not the image itself, as a deleted file will not show up in the category. Alternatively, just add the name of the file to the category.