To have keyframes after your frame 416, you need to also extend the sequenses (yellow lines where the keys are “attached” to).
I guess all you need to do is select all keyframes and drag the red little handle to the right all the way to frame 500.
The animation will then be scaled to fit the new length. If there is no “last” key frame at 416, you might put a fake one there first, then drag.
Cheers
Lennart