pks are sequential. If you sign up as 1992 they have 1992 customers. Does not follow. Only follows if: - PKs are sequential - and PKs are non-zero non-negati

pks are sequential. If you sign up as 1992 they have 1992 customers. Does not follow. Only follows if: - PKs are sequential - and PKs are non-zero non-negative - and they have not been reset at any point (or the sequence generation otherwise modified) - and all preceding PKs are those of customers (as opposed to test values, invalid PKs due to a sequence number that was generated but the registration did not complete, or customers who have since left the service) If PKs are sequential and natural and the sequence has not been modified, then you know there are no more than 1992 customers. Not exactly 1992.