Why carronades were omitted from nominal gun ratings

Why did the Royal Navy sometimes leave carronades out of a ship's official gun rating?

Because carronades could not perform the long-range fire then treated as the critical measure of a rated battery.

Nominal ratings emphasized the long guns that could fight at distance. Carronades added heavy short-range striking power but did not provide the same reach. The Admiralty could therefore classify a ship by its long-gun battery while leaving several carronades out of the headline number. This convention explains why sources may give apparently contradictory gun totals for the same frigate.