Somewhat relevant and related.

>“So, it’s a bug in Lotus 123?”

>“Yeah, but probably an intentional one. Lotus had to fit in 640K. That’s not a lot of memory. If you ignore 1900, you can figure out if a given year is a leap year just by looking to see if the rightmost two bits are zero. That’s really fast and easy. The Lotus guys probably figured it didn’t matter to be wrong for those two months way in the past. It looks like the Basic guys wanted to be anal about those two months, so they moved the epoch one day back.”

https://www.joelonsoftware.com/2006/06/16/my-first-billg-rev...