I saw a used OM-03 online for sale over the weekend, and it had a signed label. Then I noticed that the brace that usually goes along the inside of the backwood's center seam was not there. This is the brace that the label usually gets placed on top of. Is this typical of the OM build? Just looked odd without the usual brace over such a long seam that goes the length of the body.

If you are referring to the back-strip, it's not critical. That's mostly there for cosmetics. Some will say it offers support of some sort but it's not a brace (check the grain direction) and I've heard a few high-end luthiers say it will not stop the back seam from opening if that's what it wants to do. It mostly creates a nicer interior look. Waterloos don't use them specifically to retain the old-school look.

 As to why Larrivee wouldn't use it, I'm not sure why they have it on some models and not others. It's not for cost as I just looked up some pics of high-end Larrivees that didn't have one. There's a D10 Braz on Elderly right now without one.

Yes, the back strip. I guess for me it comes down to a psychological comfort to see that nice spruce strip covering the wood join. I'm also one of those people who uses too much tape when closing up a box for shipping...