A couple of things to note.
First, I have found the hot keys for copy and paste inconsistent when in the curve editor. So try using the menu choices under edit (not the main interface edit but use the timeline’s).
When you copy a track’s keyframes they will add to the keyframes already there. So the track must be clear (except for a keyframe that the time marker is sitting on).
You can’t always copy one type of track to another. So a rotation channel can’t always be copied to a position channel. Nor can an X get copied to a Y all the time.
You can also use Expresso to map an objects track to another objects track. This has the advantage of “change one and many change” and you can map any kind of track to any other kind of track (you may get weird results as rotation radians get turned into position data but that can be fun too!)