[unboggling]

After a metadata download on selected books, you've got ISBN, click that in Book Details panel and you link to WorldCat, which often shows a brief subject entry or will give you a list of books by that author, including pubdate for each listed edition. You can also click "View all editions and formats" which list also gives dates.

For popular authors of most genres, Wikipedia is often okay. Wikipedia is the default author-link-template when calibre is first installed (Prefs/Look&Feel/BookDetails tab), which links to Wikipedia by clicking author's name in Book Details panel.

Sometimes author-sites are good.

There are probably good specific sites for each genre, though I don't know most of them except SF & Fantasy. Googling may help. Links from Wikipedia entries on specific genres may help.