reverse gear

Can somebody tell me if the puntos reverse gear uses 1st gear by means of a reverse cog on the input shaft.
As i couldnt find any obvious reason for losing reverse with the old box im wondering if the problem was maybe the 1st gear not cooperating.i know reverse is on the same selector fork as 5th and that went in fine but would like to get to the bottom of why that reverse would not engage......
the ratio for reverse and 1st is the same at 3.909:1 hence the thought it was basically 1st gear literally spinning the other way......

I dont know the answer but cant see how it could be. In essence for the gear to rotate the otherway the engine would have to stop and go the other way

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Im sure pete (drevil) lost reverse and it was just a bolt had come loose retricting movement of the selector inside the box

I lost 5th.