grease pencil additive strokes

lets say i created a grease pencil strokes on some key frames from 1 to 10 without the additive stroke enabled !! how to make all the created strokes which scattered along the timeline from 1 to 10 to be visible all at once [not onion skin]

lets say i want all created strokes to be visible at keyframe[10] at the dope sheet ?? i tried to scale all the strokes key-frames from [1] to [10] to key-frame[10] or scale them all to keyframe [1] but seems that some strokes override others there would be nice if the additive effect option can be found at GP layers if the strokes are already created and the user want to change them into additive strokes