have a kid who was there and who is very much convinced -- as is most everyone else I've talked to -- that it varied a great deal from unit to unit (or Commander to Commander, sometimes but not always synonymous with the unit) in the '03 to about '05 period. He was there fall of '03, spring '04.

I think most are using 05 because that appears to be about the time the whole Army got it. I suspect it also has a little to do with the departure of Ricardo
Sanchez in Jun of '04 and about six months for Casey to make an imprint and with the rotation cycles, OIF 3 was the first rotation that had been 'COIN trained' prior to deployment if my memory serves (always a dicey proposition...) and it was the one that took 3d ID back in a different mode than had been their first trip.