No tennis match necessary.
Yes I did the search you mentioned.
Most of the sites do not post any references, they all repeat the same information, obviously copying from the other. One site did say there was actually very little research done on this subject but...
Yes the info that did pop up was eye opening.
However I will stick with my original post: "There are many varieties of true bamboo grown for food & timber. I would ***guess*** most true bamboo would be eadible (edible) to a tortoise as a small part of a varied diet."
The secret to any tort diet (or human diet for that matter) is small quantities of many different items. Wild tortoise eat many plants that are potentially poisonous, but in small quantities. Some even eat - gasp - animal protein which many people expressly forbid for tortoises.
Another factor is that most studies deal with mammal or specifically human metabolism. Reptile metabolism is much different. Many reptiles can eat plants that are dangerous to humans with no obvious affect to the reptile. I too would avaoid anything that is obviously dangerous to torts.
All things in moderation.