Defensive Stance and Side Step both have "once per round" with an Activation time of "Maneuver," so that's at least a couple instances of talents specifically saying you can't trigger them multiple times at the same activation. Jump Up and Let's Ride both cite "once per round" as each talent lets the PC convert a course of action that would normally cost them a maneuver into an incidental. The various "Natural X" talents all limit them to "once per session" given how powerful a complete re-roll of the dice can be.
Otherwise, the designers were likely figuring that the reader would apply a dose of common sense and assume that a talent can, generally speaking, only be activated once per triggering event, be that an Out-of-Turn Incidental (such as Dodge or Parry or Reflect) or a Maneuver (Center of Being) or an Incidental on their turn (Quick Movement).
It's been said since the EotE Beta that unlike some other Big Box Company RPGs (like D&D and Pathfinder and Rolemaster), the designers for this system didn't feel it was necessary to spell everything out, and presumed the people reading and playing the game were fairly intelligent, and upon being lead to water wouldn't need additional encouragement to drink.