Words related to theme

[JBAdamsJr]

I have found four small generic words that relate to a 20th-century historic event that I could include in four longer words to be my primary four symmetrically placed theme words. Would that be all I need to make the puzzle a "themed" puzzle? Or would it make it too easy to determine the theme if I included other words related to the country where the event took place, words for the month, day and year it took place, or words related to the city or area of the country where it took place?

[mmcbs]

The customary practice is NOT to include additional entries related to the theme that are not part of the symmetrical theme set. It is permissible to have an extra theme entry that serves to "reveal" the theme, and this is usually placed near the bottom of the grid. However, if the theme entries are fairly obvious, the reveal entry isn't really needed. Most editors also use titles for their puzzles, so the theme can be hinted in the title as well.