I think the most that is allowed in lying about fish is to add one inch for every year that has gone by since you caught it. So it takes a whole year for a 39 inch fish to "grow" to 40 inches. In ten years however , all those 32 inch fish can "grow" to 42 inches. Unless of course someone else is really stretching it and lying through their teeth. In that case , you can keep up with them.
Its actually best to try to keep yourself in touch with reality by being honest but many have trouble doing so.