If it had been up to me, I would have included a proper real-time-clock in the design and done things a lot differently.

But the device was designed by one company and the BLE and processor module by another. For some ungodly reason neither trusted each other, so nobody was given access to the firmware source on either side. I worked for a third company that was their customer paying the bill. I was allowed to see the firmware for both sides, but only read only, on laptops provided by each company, one at a time, in a conference room with their own people watching everything. Yeah, it was strange.

I was there because the MCU and the BLE processor sometimes glitched and introduced random noise. Turned out the connection between the two parts were unshielded UART with no error detection/correction 🤦🏻‍♂️

It was concidental that we hit the date glitch. Took all our effort just to get them to add a checksum and retry. The tiny MCU was maxed out of space. No way to fit in any more code for date math.