Historical clue formulations

• Problem in the Tower of Babel story — 2018-06-23
• Communication problem ... illustrated literally by the black squares before 5-, 19-, 26-, 54-, 65- and 73-Across — 2016-12-12
• Foreigner's obstacle ... or a hint to hidden words in 17-, 29-, 37- and 49-Across — 2014-08-13