The Unix/Linux date command will accept no date before 01 Jan 1970 or after 2038.
So the date command is not appropriate for your purpose. There are other ways - i'm sure that someone will advise you appropriately.
put in a file called myfile 19700101 and run this code
echo $(date -f myfile)
Change the date to before 1970 to check what I say. then try after 2038 (not sure what month day)
I think Reverse's previous comment was pointing out that you were probably looking for a format +%Y%m%d YYYYMMDD, but instead of the day you put %A which is the weekday. I only explain that because it took me more than a few moments. Sorry Reverse, I'm a bit slow tonight!