Mentioning Deals I Follow

Hi,

When I mention a deal I'm impressed by in a cover letter or interview (for a firm), do I only reference completed deals, or are announced deals also okay? Does it matter if a firm is one of many financial advisors in an M&A transaction, or is it better to mention one where they are the sole advisor to a buyer/seller? What is the oldest amount of years that a deal would still be relevant when I mention it? Thanks