Never reuse a clip, it must be replaced every time you remove it...
Sounds ridiculous, as there is no real stress on that part, but vibrations can do some funny things.
I feel that after running a clip in an engine and subjecting it to the temperatures that combustion can throw at it, it can alter the spring properties.
When you remove and refit an old clip, surely the clip will not be at its optimum holding strength.
When you remove a clip from a piston pin hole, there may be a build up of deposits where the gap in the pin does not fit in.
If a new pin is fitted, it may not completely seat due to this build up if not fitted in the exact position the former one was taken from.
Always check the retaining groove for build up before fitting a new clip.