Planned, announced, ordered, and built are different fleet counts

Why is the County class sometimes described as a planned class of sixteen ships?

That figure reflects announced or contemplated ships, while the numbers planned, formally ordered, and actually completed need not match.

Several procurement stages are often flattened into one number. A navy may study or announce ships that are never funded, place orders that are later cancelled, or build only part of a larger programme. The County-class total therefore depends on which stage a source is counting. Class histories need to define what planned means before their totals can be compared.