Find all possible dates
Ruby, 234 bytes



require'date'
a,b,g=%w(%Y%-m%d %Y%m%d %Y%-m%-d %Y%m%-d %-m%d%Y %m%d%Y %-m%-d%Y %m%-d%Y %d%-m%Y %d%m%Y %-d%-m%Y %-d%m%Y),Date.new(1920)-26,gets
(b..b+36524).map{|d|puts d.to_s if(a+a.map{|x|x.tr(?Y,?y)}).map{|x|d.strftime(x)}.member?g}


Try it online!

I'm willing to bet that this can be shortened this significantly (with regex maybe), but I'm not clever or knowledgable enough to figure that out.

If we are allowed to print the date object itself instead of a string, change puts d.to_s to p d.