Strange, I’ve never noticed this before but the Mac and iOS/iPadOS versions of the Calendar and Mail icons are different. Apparently (pun intended) I need to be more observant. 
Keynote and Numbers are identical.
ON THE MAC
ON THE IPAD
I checked preferences but I don’t see a toggle to change the icons on the Mac.
Talking about a First World problem! 
I wonder why we need to know the day of the week while working on the iPad but only the month on the Mac…
I’m sure there’s a philosophical paper waiting to be written on different concepts of time between Apple devices.
I’m thinking the iPad versions are new and they just never got around to updating the Mac icons but that seems strange given that Pages and Numbers icons are identical. I can’t imagine it is an oversight. Hmm, this an interesting, albeit profoundly unimportant, matter. 
What has been seen cannot be unseen. I’m not sleeping tonight.
That made me laugh. 
I’m out. Back to Windows and Android!
Unleash the internet! 
After all these years, I’ve honestly still not learned to “see” the date on these icons. Only the clock on iOS/iPadOS and the calendar on all platforms display information like this. The thousands of other apps have to make do with badges or nothing, so my brain will simply not process the information is even there.