Okay. Why do you doubt them? Any number of military men such as De Verner and Clausewitz stated that volley fire can [and should] be opened up at 200 paces. Any number of observers, friend and foe state that skirmishers shot at each other at that range. Even Oman states in several places where the French opened up with volleys at that range or greater, such as Talavera. Most ordinance tests like Muller's give a 30% to 40% hit ratio at 150 yards. [certainly under perfect conditions, degraded in battle for sure, but even halved, that is 20 hits out of 100, or 80 men casualties out of an opposing battalion of 500. Better than 10%]
So ordinance tests give the performance of smoothbore muskets
Military men state that 150 yards is within 'effective range' and considered a combat range for smoothbore muskets.
There are numerous reports from both French and Allied observers of being fired at..at that range
And while most distances were estimates, the amount of time given by necessity to judging distances [particularly by the pace] during the Napoleonic wars, I doubt that such estimates were all the inaccurate.
I think sometimes the British propensity for holding fire has colored our view of when all fire was held or should be considered effective. Certainly, the smoothbore was an inaccurate weapon, but it is the reports on how it was used and should be used that tells the tale.