Can published historical warship speeds be assumed accurate?

Can published speeds for older Royal Navy ships be assumed to reveal their true maximum?

No. Concealing maximum performance limits an enemy's ability to match a warship's speed or predict its movements.

Revealing a warship's true maximum speed helps an opponent design ships to match it. Accurate performance knowledge also helps an enemy anticipate movements at both strategic and tactical levels. There is therefore reason to doubt that published figures always disclosed the full performance of older Royal Navy ships. Merchant lines had a different incentive, since speed helped sell their services.