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I don't know if all Yamahas are created equal but one Yamaha I fixed had one of those improperly glued bridge that looked as though it was pasted onto the wet finish with the dry finish still under the bridge, so the bridge didn't get fully bonded to the soundboard.

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Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Sure it does. Even jointed and sanded wood has open pores. Wood glue grips into those pores.

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Another day, another dollar.

What Todd said.

AS I understand it, the strongest glue joints have between .002" and .008" of dried glue in them. 'Keying' just makes deeper scratches that end up being thicker glue lines than the optimum. Smooth, well fitted surfaces are what you need to keep the bond thickness in the right range.

I was told that the Forest Product Lab, in a study of wood aircraft structures back in WW II, found that surfaces that had been worked within 15 minutes of gluing ended up bonding better. That's the 'high surface energy' Todd mentioned: working the wood breaks chemical bonds, which take a while to re-form, and if you put glue on those open bond sites, you get a better joint.

The test for surface energy is to spray it with a mist of water. If it spreads out into a film the surface energy is high: the polar water molecules are attracted to the open bond sites. If the water forms droplets the energy is low. I tried that on a fossil mammoth ivory bridge. The stuff is notably hard to glue, and I suspected it might have naturally low surface energy, since most of the chemistry will have already happened. Sure enough, a surface even a few hours old caused the water to bead up, while it would spread out on a fresh surface. I gave the gluing surface a quick scrape just before spreading the HHG on it, and so ( about two years) far it's held.