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clapper sync.

I have a "dumb" question about clapper sync.
My lab has synced DAT's in the telecine. The clap sound often overlaps two frames. (ie. the sound will start in the middle of one frame and then extend to the next)
If the audio "clap" starts to happen at the tail of the first frame, when the clapper sticks do not appear to be together yet, is that necessarily a lab mistake? Most of the clap sound is heard on the second frame where the sticks are visibly together.
I'm thinking this is by design. Because, although the sticks aren't together in the frame, there is 1/48th of a second where the camera is loading the next frame and the clap could have happened then. I know that in FCP I can shift the audio sample but this may not be a mistake at all.

Maybe the diagram below explains.
"A" is the frame number.
"B" is whether the camera shutter is open or closed
"C" is the audio clap.
In frame 1 the sticks are not together
In frame 2 they are.
Frame 1 appears with sticks open but "clap" can still happen while shutter is closed and the camera is loading the next frame.

A        1             2            3            4 
B        -Open--Closed-Open--Closed-Open--Closed- 
C        -----------XXXXXX-----------------------