Continental Provincial Infantry

I would leave it alone. Provincial infantry are good fun to use and tonight they gave the British flank march a beating. They are inadequately trained or armed regulars (or, conversely, better trained and equipped militia!!) so serve well when not used recklessly, keep your generals in support and always have a few bonus rally cards up your sleeve. When they retreat or get isolated then a volley can be enough to see them break and run. I thought the Cowpens scenario may have some British Provincial infantry instead of so many Regulars but there you go - just my interpretation. Remember that the Provincial infantry don't benefit from the bonuses that Regular Infantry get from the cards such as Regular Battle Bonus and the extra dice for the Bayonet Attack.

Play twice is the general convention.

Just looking over the Continental OB for Long Island
en.wikipedia.org/wiki/Order_of_battle_of...attle_of_Long_Island

far more "Continental" regiments than I expected, though looking into the details they seem to be really Provincial regiments re-titled as Continental Army. e.g. the 8th Connecticut Regt was made the 17th Continental Regt in 1776, though the expiry of enlistments makes it difficult to say it was even of similar composition.

So I'd guess there is some design for effect in the scenario OB, and for that reason I'd tend towards leaving it alone.

Agree that it makes for balance.
I do recall that in the case of Memoir 44 the point was made somewhere that the scenarios were not always balanced because the history was not. The suggestion was that each scenario was played twice with the players changing roles for the second game.
That would work here as well I guess.

I think you have the history right, though whether it was rather the lack of bayonets rather than training I'm unsure.

However, these two scenarios seem pretty pro-British anyway, so I don't see that downgrading the Continentals will help play balance
boardgamegeek.com/thread/1877043/initial...hts-scenario-balance

I have been playing the Long Island scenarios which predate the Valley Forge period.
There seem to be a lot of Continental Provincial Infantry which in melee kill on crossed sabres. But my limited reading of the history suggests that at this time the Continentals were rather wary of melee with British Regulars and not yet adept with the bayonet.
Playing the scenario of the Flank march with the rule for Provincials changed so that they are not able to kill in melee on crossed sabres gives a fairly historical outcome; but it is decidedly unbalanced in favour of the British.
Is there an argument for adjusting Provincial melee capability depending on the date of the action? Or is it best to leave it as it is in order to produce a more balanced game?