Possible Clues:

• Big name in book publishing ... and what each starred clue's answer contains?
• Publishing company whose name serves as a hint to entering several Down answers in this puzzle
• Big name in American book publishing for 120+ years ... and a hint to the answers to the starred clues
• Supposed inventor of baseball ... or a hint to 17-, 26-, 36- and 50-Across
• Big name in publishing, and a visual hint to the three adjacent pairs of answers to starred clues