It does in fact matter who turned "you", from the undead perspective (all too often ignored...). Should that person, and only that person, approach within ten feet, you are no longer turned. So, there is a portion of the "state" of being turned that is a relationship between two creatures, and it is always necessary to track which Cleric turned which undead. An argument can be built on those facts.
It does say that turning capacity does not have to be wasted on turned undead. The context appears to be during repeat tries by the same Cleric on the same, ah, pack of undead. They should probably have mentioned multiple Clerics- not that rare of a situation.
What is seems to boil down to is should two roughly equal clerics expect to get double the turning results, by not overlapping, or just better results? The odds are they will turn somewhat more, maybe even twice as many. Should turning twice as many be a given?
I think turning is individual, and stacked results for a group of Clerics is too much. It can certainly be argued the other way, as there isn't anything specific. But maybe there would be if you could stack.
The aid another idea is interesting- I don't think that is in the rules, though.
Also, isn't it the case that the flank bonus applies to the attacker, not the defender- you aren't flanked, you are flanking?
