I wonder if the quality of wood varies between companies. By this, I mean if you take the same wood type, but they have different properties on kendamas from different companies (e.g. durability, grain, etc.). If ever, this could be attributed to their wood supplier, or their overseas manufacturing methods. I'm asking because I have two ash kendamas from KUSA (OG TJ mod and an Ash 2.0) and KROM (Nihon ash and Thorkild mod). I play the same style on both of them, yet my KUSA ash kens always chip easily while my KROM kens are as strong as ever.
You definitely notice a difference, especially from dama brands/companies known to hand turn/machine the damas themselves. Zebrano is a good example. My first was a Lion Head zebrano dama which has a grain more similar to DWI and the recent Sweets zebrano woods, but these 3 have a very different grain than KUSA zebrano (I’ll post a pic when I get the chance).
Not sure if it’s 2 different species of zebrano wood or if one brand is finished differently than the other but you can see a pretty clear difference between one zebrano ken and the other. AFAIK, KUSA is the only company that offers a solid, one wood piece zebrano tama. I’ve had 2 Lion Head zebranos total and saw the stock the kiosk cart had in my area and all the tamas were made of 2, even 3 pieces of separate zebrano wood laminated together.
The companies don't all get their woods from the same place so of course some wood will be different than others, even if they're the same wood type. A maple 2.0 isn't going to play the same as a maple GT-1 because the wood itself is from different places, even though they're both maple. That's why your ash 2.0 and your ash dawg play differently and break in differently. I think it also has to do with how the wood is stored and cut and everything.
There is actually a system for Grading Hardwood Lumber but I don't know if it comes into play when most kendama companies make kendama (or have them made). Raw materials chosen for many products end up being selected for the lowest cost based on the likelihood that it will pass the requirements for the end product. For example many knife makers produce blades without claiming anything other than "stainless steel" so they are free to use whatever is adequate for the job and cost effective for their product. Higher end makers or specific models, on the other, hand tout specialized steels in their knives to draw a different clientele who will pay the additional money for their product. Also as mentioned previously trees are living things without the exacting quality controls that can be enforced on "made" things like steel. Location, weather, processing, and production techniques can all effect the final product. Just taking the variance in one tree shows vastly different wood from the heartwood out to the sapwood; now multiply that times thousands of trees. EDIT: Here's a screen cap from the site linked above. Look there for descriptions of each grade.