Arun Venkatesan put together a really nice visual history of the System Preferences app, from Mac OS X 10.0 through MacOS Big Sur. I particularly appreciated this explanation of the two different dates often seen in Apple’s calendar-related icons:
Since the Public Beta, the calendar in the icon has shown an 18. 10.10 added the month of July to the icon. July 18 likely refers to the day that the Mac OS X Public Beta was first announced at Macworld New York.
In Big Sur, after 20 years of showing July 18, that icon has changed to July 17, likely to conform with the Calendar app icon. iCal, as the Calendar app was previously known, was first shown to the public on July 17, 2002.
I knew the dates had to refer to something — these things are never random — but I had no idea what. This is good trivia.
Update: Venkatesan also says that the Energy Saver preference panel is replaced with a “Battery” setting in Big Sur, but that is not the case for desktop Macs. Energy Saver retains its name and LED lightbulb icon.