Couple of battle questions.

[Jxrc]

Does anyone have any ideas about whether allied forces that unite against you all come under the leadership of the one general that is shown at the battle info. screen or whether they are independently linked to their respective generals?

Logically they should come under the leadership of their own general each. I have never tested it but I am pretty sure that if you kill one of the enemy general only the units of its factions will be affected. This is hard to see in normal battle because units get a moral malus for seeing their allies run away but I have had bridge battle where the first army's general was killed (so that his army ran away) while the second allied army fought normally

Does a high valour unit, say 7 or 8, perform better under a no star general than a vanilla unit under a 7 or 8 star general?

An eight star general will only add 4 to the valour of the units under his command so that a vanilla unit will never reach 7 or 8 thanks to the general.

That being said, I have a hunch that a unit with an actual valour of 1 will perform better than a unit that has its 0 valour increased up to 1 thanks to the general. No had evidence supporting that view, just a feeling I get after quite a few battles with the vikings in Norway where valour 1 vikings seems to do better in head-to-head clashed that mine lead by a four star king.

Also are the flanking bonuses cumulative, ie. Is it worth charging from behind with one small unit then another? Or is it better to throw a large unit into the rear and swamp them with numbers?

Best solution is to throw two large units

If that's not possible, my guess is that two small units are better. Even though they kill pretty much the same number of men as one big unit, moral penalties should had up at least if you attack from one flank and the rear (not sure that being attacked on both flanks trigger a double penalty)

Finally, I only have VI, and have been a player for ages, but, is the 're-training of units' an XL thing or am I missing something obvious that I should have picked up in the walkthrough four years ago...!

Not sure what you mean. Retraining is useful even when the units have suffered no losses if one of your province gives a valour bonus or add better armour weapon. For instance, if you play as the Danes and have produced Viking in Danemark, it might be worth retraining those in Norway to get the valour bonus and then in Sweden to get the weapon upgrade. That's pretty much all there is to it. You could also retrain an unit in province where a morale enhancing facility has been built but if that's the only bonus granted by that province its pretty hard to keep track of which units have been so upgraded. Can be useful for some low morale units like spearmen though so that I would suggest just to wait for a few more turns, build some structure granting a visible upgrade (armor, weapon) so that it's easy to see that units without that upgrade do not benefit from the morale bonus granted by the church (or any other relevant religious building).