When I read a scientific paper I usually would like to know the point in time when it has been written or publicized. I would expect such a date written near to other meta data like the the author's names.
Unfortunately often these papers lack in such a date. I can't see why. Okay such a paper may be the work of years, but it is publicized at a single point in time. When I wrote my thesis I wrote down the date when I have submitted it to my university for approval.
Such a date is very useful for finding, classifying and evaluating papers.
An example would be this: https://www.cs.ox.ac.uk/files/6487/pwvault.pdf
The papers I read are in the field of computer science. This may be different in other areas.