You'd know better than me, being a QFI, but the retreating blade stall sound is a dagga dagga dagga when you are low, fast and going round a corner a bit sharp. You fix it by dropping a bit of collective, or you end up rolling nose down heading in the direction of travel of the blade. At least thats what I was told 30 odd years ago, and as I've said I'm always prepared to be wrong.
Retreating blade stall will invariably lead to an initial pitch-up, not pitch-down. You are correct about needing to gently reduce the collective. If the pitch-up and/or reduced collective does not 'unstall' the retreating blade (reducing AoA), the helicopter will try to roll towards the retreating blade, ie for the Puma a roll to the right.