You've heard of Y2K and the 2038 problem, but what about the 1975 problem?
The UNIX form letter generator converts the current date to a string, but it only handles 1974. Why isn't it more general?
Well, the form utility was written around 1971 when UNIX used an a different unit for time, jiffies (60ths of a second) since the epoch instead of seconds since 1970. This 60× precision caused times to overflow a signed 32-bit integer every 13.6 months, so the epoch was bumped yearly. This yearly ritual of modifying the kernel meant it wasn't worth generalizing to support any year.
An earlier version of form uses jiffies since a 1972 epoch. The version from UNIX V4–V6 does the bare minimum to update it to the new system of seconds since 1970, while keeping the yearly overflow.
