Creature into Creature. (...) the new form can be any kind you choose. The target's game statistics, including mental ability scores, are replaced by the statistics of its new form. It retains its alignment and personality. (...)
The creature is limited in the actions it can perform by the nature of its new form (...).
Let's say a high level player (wizard, bard, etc) casts True Polymorph to change an ally into another creature with legendary actions (such as a dragon, a mummy lord, a vampire, etc). Would this ally's form change into the complete stat block (excluding alignment and personality) of the new form? Would the ally thus be able to use the new form's Legendary Actions? If not, which rule would prevent that?
According to MM 6 "stat block" of a creature means the same as its "game statistics". This suggests that the answer to my question is a yes. However, Legendary Actions are not mentioned in the section listing what's part of the stat block (MM 6-11), under header Statistics. They are only mentioned under header Legendary Creatures. Is there a reason for this?
My common sense tells me that I should ignore this typographic detail. Just making sure there's no rules preventing players from getting Legendary Actions.