Common or Boat-tailed Grackle Nestling?

Someone brought in this almost-fledgling grackle to the emergency veterinary hospital I work at. We always get a lot of kidnapped babies this time of year. We're all tired of driving to the rehabber place, so I am going to feed this kid until it's ready to raid the wal-mart parking lot ;). I think it should be able to stay outside but with access to it's "nest" box and food in another week. Anyway, I was wondering if anyone knows how to differentiate (at this age) between a Boat-tailed Grackle (Quiscalus major) and a Common Grackle (Quiscalus quiscula)? It will be fun to see what it grows into. Here are some pics. BTW, I have done this before, but only with raptors. Hopefully the grackle is as hardy, they certainly do seem to be!

Boat-tailed Grackle can be ruled out in your area based on the range map, so it could either be Common or Great-tailed.
http://www.allaboutbirds.org/guide/Boat-tailed_Grackle/id
I am not sure I'd want to try to give an identification on one so young. Maybe another will know these young birds. We only have Common that nest on our property. For our area of Iowa, the breeding habitat of Great-taileds are limited to marshy areas.

Oops, confusing Great-tailed Grackle for Boat-tailed. A local name for the Great-tail here is "Rudder-tail" after a boat's rudder, hence my confusion. Great-tails are all over the place here, I see more than Common Grackles. I call them both Wal-Mart birds.
I knew it would take a well-versed person to be able to differentiate in one so young, maybe counting number of primaries or some such. I just can't help but get excited over wildlife. :)

Any new photos? Might be easier to identify now with a bit more feather growth.

Resin