We had a classic situation at a software house I worked at in the '80s - employee numbers were 1-999 and then jumped to 5,000 - because, you guessed it, this "u

We had a classic situation at a software house I worked at in the '80s - employee numbers were 1-999 and then jumped to 5,000 - because, you guessed it, this "unique" field was used with magic numbers 1,000 - 5,000 being reserved for project ids in various key accounting systems! And we were supposed to teach our customers good design principles...