When it's Neue Haas Grotesk.
Font Bureau recently released a digital version of the real Helvetica. Yes, that typeface which is a superstar of modernism, the feature of a documentary, both loved and hated by designers, and used in kor's own identity is in fact not an exact reproduction of the original typeface designed by Max Miedinger. The Haas type foundry designer created Neue Haas Grotesk in 1956-1957 for hand-set type. The name change, and design changes, occurred when his design was translated for Linotype and later for other print technology advances (film and digital). Font Bureau has a fantastic description of the history of Neue Hass Gtoesk/Helvetica and it's recent revival. But beyond the particulars of this typeface's history, the release highlights how perceptions of "classic" or "best" designs can be altered over time
Another example of this in action is the FontShop's 100 Best Typefaces of All Time website. You can only image the debates that this list can cause! Of course, there's even a place for not so heralded typefaces. Even the much maligned Comic-Sans has it's place because - to steal a line from the Comic Sans Project - Neue Haas Grotesk is so 2012.