Excel has the "feature" that anything remotely looking like a date is forcefully converted to a date. It usually is not possible to figure out which string was originally input. Also the data type of the cell is off then.

My first encounter is with CAS registry numbers (see https://en.wikipedia.org/wiki/CAS_Registry_Number)

The problem is also in genetics: https://genomebiology.biomedcentral.com/articles/10.1186/s13059-016-1044-7

btw. open office fully reimplemented this feature - also without being able to turn it off.

A nicety it that this conversions is not only applied to manually input data, but also to pasted, and - to make things fun - to data written by apps using excels COM interface.